THE  NORMAL  AND  PATHOLOGICAL 
HISTOLOGY  OF  THE  MOUTH 


VOLUME  I 
NORMAL  HISTOLOGY 


BY  THE  SAME  AUTHOR 

"AN  INTRODUCTION  TO  DENTAL  ANATOMY 

AND  PHYSIOLOGY:  DESCRIPTIVE 

AND  APPLIED,"  1913. 

"DENTAL  MICROSCOPY,"  A  HANDBOOK  OF 

PRACTICAL  DENTAL  HISTOLOGY. 

FIRST  EDITION-,  JANUARY,  1895. 

SECOND  EDITION,  JULY,  1899. 

THIRD  EDITION,  MAY,  1914. 


PART  EDITOR  OF  TOMES' 

'A  MANUAL  OF  DENTAL  ANATOMY' 
SEVENTH  EDITION,  1914. 


PL  A 


The  Vascular  3upp 

during  Dev-  . 


DESCRIPTION  OF  PLATE  I 

Sagittal  section  through  the  mandible  of  a  kitten  at  birth.  The  vascular  system 
is  injected  with  Prussian  blue  solution.  Tissues  hardened  in  alcohol.  Section 
stained  with  carmine.  Magnified  20  times.  A.  Internal  set  of  bloodvessels 
supplying  the  dental  pulp;  B.  External  set  to  the  enamel  organ;  c.  Vessels  of  the 
gum;  D.  Of  the  alveolar  wall  and  dental  capsule;  E.  Internal  anastomoses  of 
external  set  of  vessels;  F.  Point  of  junction  of  external  and  internal  systems. 
For  details  see  pp.  134  and  262  et  seq. 


The  Normal  and  Pathological 
Histology  of  the  Mouth 

BEING  THE  SECOND  EDITION  OF 

The  Histology  and  Patho-Histology 

OF  THE 

Teeth  and  Associated  Parts 


REVISED  AND  ENLARGED 


BY 

ARTHUR  HOPEWELL-SMITH 

L.  R.  C.  P.,  LOND.,  M.  R.  C.  S.,  ENG.,  L.  D.  S.,  ENG. 

PROFESSOR   OF   DENTAL     HISTOLOGY,    PATHOLOGY     AND     COMPARATIVE   ODONTOLOGY 
UNIVERSITY    OF     PENNSYLVANIA,     PHILADELPHIA;     JOHN     TOMES    PRIZEMAN    OF 
THE   ROYAL   COLLEGE     OF    SURGEONS    OF     ENGLAND;    MEMBRE   HONORAIRE 
DE    LA   SOCIETE    ODONTOLOGIQUE    DE     FRANCE;     FORMERLY   LECTURER 
ON   DENTAL  ANATOMY,   SURGEON   AND   DEMONSTRATOR   OF   DENTAL 
HISTOLOGY     AT     THE     ROYAL    DENTAL     HOSPITAL    OF    LONDON; 
MEMBER   OF   THE   FACULTY   OF    MEDICINE   OF   THE   UNIVER- 
SITY   OF    LONDON;    EXTERNAL   EXAMINER    IN  DENTAL 

SURGERY     AT     THE    UNIVERSITIES    OF   BIRMINGHAM, 
LEEDS    AND    LIVERPOOL;    LECTURER  ON  DENTAL 
SURGERY     AND     PATHOLOGY     AT   THE   NA- 
TIONAL DENTAL  HOSPITAL,  LONDON 


VOLUME 


NORMAL  HISTOLOGY 


WITH  2  COLOURED  PLATES  AND  262  ILLUSTRATIONS 

IN  THE  TEXT,  INCLUDING  149 
ORIGINAL  PHOTOMICROGRAPHS  BY  THE  AUTHOR 


PHILADELPHIA 

P.  BLAKISTON'S  SON  &  CO. 

1012  WALNUT  STREET 


COPYRIGHT,  1918,  BY  P.  BLAKISTON'S  SON  &  Co. 


WBJ1A-L   DEPARTMENT 


THK     M  A  I>  1>  K     I'RKSS     YORK     PA. 


LLVP  VV/U 

101 

V,'  W7 


oo 

SIR  JAMES  CRICHTON  BROWNE,  M.D.,  LL.D.,  F.R.S. 
J.  HOWARD  MUMMERY,  Sc.D.,  PENN.,  M.R.C.S.,  ENG.,L.D.S.,  ENG. 

AND 

FREDERICK  J.  BENNETT,  M.R.C.S.,  ENG,,  L.D.S.,  ENG. 

AS   AN 

EXPRESSION 
OF  THE  ESTEEM  AND  SINCERE  REGARD 

OF 


PREFACE  TO  THE  SECOND  EDITION 

OWING  to  a  completer  extension  of  the  subjects  included  in 
this  work,  it  has  been  considered  necessary  to  change  its  title. 
The  present  one  more  correctly  represents  its  scope. 

For  the  convenience  of  the  reader  the  book  is  now  issued 
in  two  volumes.  The  first  relates  to  the  Normal  Histology 
of  the  Mouth  and  its  Contents,  and  the  second  to  the  Patho- 
logical Conditions  found  therein,  with  special  reference  to  the 
Teeth  of  Man.  Part  III  in  that  Volume  records  the  latest 
observations  of  the  dental  tissues  at  times  encountered  in 
ovarian  teratomatous  cysts. 

A  thorough  revision  of  the  First  Edition  has  been  effected. 
Six  additional  chapters  appear  in  Volume  II,  being  specially 
revised  accounts  of  original  researches  undertaken  by  the  author 
in  recent  years.  Chapter  XVII,  Vol.  II,  contains  part  of  a 
paper  presented  by  Mr.  MacAdam  Eccles,  M.  S.,  and  the 
author  to  the  Royal  Society  of  Medicine  of  London.  The 
substance  of  the  chapter  dealing  with  "Pyorrhea  alveolaris" 
was  originally  submitted  to  the  Xlth  International  Medical 
Congress  at  Buda-Pesth.  The  illustrations  remain  unique. 

Supplementing  those  first  described  in  the  First  Edition. 
originality  can  be  claimed  for  the  observation,  investigation, 
recording,  and  naming  of  several  new  pathological  conditions 
of  the  human  dental  tissues,  e.g.,  Nanoid  dentine,  Odontoceles — 
extra-capsular  and  sub-capsular — Diphyodontic  gemination, 
Hydropic  degeneration  of  the  oral  mucous  membrane.  Fibroid 
degeneration  of  the  alveolo-dental  periosteum,  etc. 

Some  changes  in  terminology  have  been  deemed  advisable 
and  needful.  Thus  "epiblast"  and  "mesoblast"  are  now 
"ectoderm"  and  mesoderm;"  the  "medullated"  and  "non- 
medullated"  nerves  become  "my clinic"  and  "amyelinic" 
respectively.  The  "dental  follicle"  is  more  correctly  desig- 
nated the  "dental  capsule;"  for  it  bears  no  histological  resem- 


X  PREFACE    TO    THE    SECOND    EDITION 

blance  to,  nor  does  it  at  all  approach  the  functions  of  such 
widely  dissimilar  structures  as  the  hair  follicles,  the  Graafian 
follicles,  the  agminated  and  solitary  follicles,  etc. 

A  description  of  the  pathological  condition,  entitled  in  the 
First  Edition,  a  "granuloma"  is  omitted  from  the  present 
volume.  A  so-called  granuloma  does  not  conform  to  the 
correct  definition  of  a  tumour,  and  is  in  no  sense  a  new  growth, 
being  merely  one  form  of  granulation  tissue,  the  result  of 
chronic  inflammation  of  the  periodontal  membrane.  It  is 
true  that  certain  diseases  such  as  tuberculosis,  syphilis,  glanders, 
leprosy,  actinomycosis,  etc.,  are  grouped  by  some  pathologists 
as  the  infective  granulomata,  because  they  give  origin  to 
formations  resembling  tumours  composed  of  granulation  tissue, 
or  at  least  a  tissue  of  closely  allied  appearance,  and  are  of 
infective  derivation.  It  is  also  true  that  some  hyperplasic 
growths  of  the  skin,  including  Mycosis  fungoi des  and  Dermatitis 
papillomatosa,  as  pointed  out  by  Weichselbaum  ("Elements 
of  Pathological  Histology,"  1892),  which  develop  as  a  direct 
consequence  of  inflammation  are  sometimes  called  granulomata. 
But  there  is  nothing,  either  from  a  clinical  or  pathological 
point  of  view,  to  justify  the  application  of  the  term  to  chronic 
inflammation  of  the  alveolo-dental  periosteum,  or  its  retention 
in  modern  dental  literature. 

One  hundred  and  sixty  new  and  original  photographs  and 
photomicrographs  have  been  added  to  the  text. 

The  author's  grateful  thanks  are  extended  to  his  friend  and 
colleague  Professor  Nathaniel  Gildersleeve,  M.  D.,  for  rewriting 
Chapter  XVI,  Vol.  II.  His  contribution  represents  le  dernier 
mot  with  regard  to  the  science  of  this  branch  of  Oral  and  Dental 
Pathology:  it  is  authoritative,  perspicuous,  comprehensive, 
important  and  valuable. 

To  "The  Dental  Cosmos"  for  the  use  of  many  illustrations, 
and  to  the  Publishers  for  their  courtesy  and  excellent  typo- 
graphical and  pictorial  presentation  of  the  pages  of  the  book 
the  Author  desires  to  tender  his  best  thanks. 
THE  UNIVERSITY  OF  PENNSYLVANIA,  PHILADELPHIA. 


PREFACE  TO  THE  FIRST  EDITION 

IN  presenting  to  the  reader  this  humble  effort  to  detail 
the  essentials  of  his  favourite  study,  the  writer  is  fully  sensible 
of  the  many  shortcomings,  textual  as  well  as  pictorial,  which 
are  necessarily  attendant  upon  such  an  undertaking.  It  is 
extremely  difficult  to  prevent  subjective  impressions  and 
interpretations  from  obtruding  themselves  here  and  there,  no 
matter  how  subsidiary  to  other  weighty  matters  the  author 
has  endeavoured  to  make  them.  The  personal  equation  is 
generally  present  and  apparent  in  all  work.  The  book  rep- 
resents an  earnest  struggle  for  an  intimate  knowledge  of  the 
truth,  clear  and  unprejudiced.  And  if  the  expressions  of 
personal  opinions  seem  to  be  rendered  too  conspicuous  they 
must  be  regarded  on  their  individual  merits,  and  tested  and 
accepted  or  rejected,  as  the  case  may  be.  The  astute  reader 
must  be  the  judge.  The  fallibility  of  him  who  now  enters  upon 
his  task  must  not  be  forgotten,  and  where  errors  have  been 
committed  they  must  be  condoned.  But  the  honesty  of  the 
writer's  purpose  or  of  his  convictions  must  never  for  one  moment 
be  impugned. 

The  establishment  on  a  scientific  and  logical  basis  of  the 
order,  sequence,  and  internal  composition  of  each  chapter  has 
been  attempted.  The  manner  of  dealing  with  the  variety  of 
pathological  facts  and  histological  data  in  Chapters  XIV., 
XV.,  and  XVI.  has  been  founded  on  two  considerations. 
First,  it  has  been  deemed  advisable  to  place  on  record  an 
intelligent  enunciation  of  what  is  implied  by  certain  words. 
Some  writers,  especially  those  of  the  Continent  of  Europe, 
are  apt  to  confuse  ideas,  the  result  being  a  constant  use  of 
some  terms  found  in  ordinary  dental  nomenclature  which 
possess  a  lack  of  uniformity  of  definition,  etc.  Second,  this 
method  of  arrangement  affords  a  convenient,  and,  therefore, 
suitable  "setting"  or  background  for  the  description  of  the 


Xll  PREFACE    TO    THE    FIE.ST    EDITION 

Mstolagical  characteristics  of  teeth  and  allied  organs,  which, 
after  all,  are  intended  to  be  the  most  distinguishing  feature 
of  the  work. 

An  acquaintance  on  the  part  of  the  student  with  the  simple 
elements  of  histology  and  pathology  is  pre-supposed. 
An  extensive  bibliographical  mass,  to  which  references 
are  made  throughout,  has  been  consulted.  In  order  not  to 
burden  the  text  with  too  great  a  number  of  the  writings  of 
many  histologists,  an  attempt  has  been  made  to  place  their 
hypotheses  on  an  eclectic  basis,  namely,  those  which  in  the 
eyes  of  the  author  are  worthy,  some  of  notice  merely,  others 
of  serious  consideration.  Many  fundamental  propositions  are 
not  universally  accepted,  and  some  of  these  are  here  noted; 
so  that  the  reader,  interested  in  any  special  branch  of  Dental 
Histology  or  Histo-Pathology,  may  receive  hints  and  be 
guided  and  stimulated  in  taking  up  original  research. 

In  this  way,  some  prominence  is  accorded  to  the  recent 
writings  of  Oscar  Romer,  who,  with  others,  denies  the 
existence  per  se  of  the  sheaths  of  Neumann.  On  the  other 
hand,  the  work  of  many  is  already  sufficiently  completed,  and 
knowledge  is,  as  far  as  can  be  ascertained,  accurate  enough. 
Thus,  with  no  fear  of  being  prolix,  the  researches  of 
Aitchison  Robertson  on  the  growth  of  dentine  may  be  cited 
extensively.  But  examples  need  not  be  multiplied. 

The  inclusion  of  Part  III. — a  preliminary  histological  ex- 
amination of  many  of  the  commoner  and  some  of  the  rarer 
morbid  affections  of  the  teeth,  gums,  and  osseous  framework  of 
the  mouth — affords  the  reader  an  opportunity  of  comparing  the 
morphological  differences  between  healthy  and  diseased 
conditions  of  the  masticatory  organs.  This  section  of  the 
book  should,  therefore,  be  read  and  studied  in  conjunction 
with  Part  I.,  and  deductions  drawn  therefrom.  The  juxta- 
position of  the  two  should  be  of  assistance  to  the  thoughtful 
and  enquiring  student,  and  serve  to  extend  and  widen  the 
area  of  his  mental  horizon. 

The  author  desires  to  express  his  indebtedness  to  the 
published  works  of  Mr.  Charles  Tomes,  and  to  Drs.  G.  V.  Black, 
Miller,  Leon  Williams,  and  Norman  Broomell,  for  the  use  of 


PREFACE    TO    THE    FIRST    EDITION  Xlll 

some  of  the  electrotypes  which  have  accompanied  their 
communications  to  The  Dental  Cosmos;  and  also  for  the  same 
to  the  Council  of  the  Odontological  Society  of  Great 
Britain.  In  addition,  he  is  grateful  for  the  loan  erf  valuable 
material  and  sections  to  many  personal  friends  at  home  and 
abroad.  Finally,  he  wishes  to  thank  Mr.  Frank  J.  Butler, 
for  his  original  water-colour  drawings;  and  the  Publishers  for 
their  unvarying  courtesy  and  assistance  in  the  production 
of  the  book. 
BERKELEY  SQUARE,  LONDON,  W. 


THE  DENTAL  TISSUES 

CHAPTER  I 

PAGE 

Prolegomena 3 

Introductory — Dental  Histology  a  Part  of  Dental  Anatomy — 
Founders  of  the  Science  and  Art — Importance  of  the  Subject — 
Historical — Problems  of  the  Present  and  Revelations  of  the  Future 

CHAPTER  II 

Nasmyth's  Membrane 9 

Definition — Views  as  to  its  Origin — Dimensions — The  Cellular 
Layer — The  Translucent  Pellicle 

CHAPTER  III 

The  Enamel 17 

Definition — Origin — Distribution — Relationships — Gross  Anatomy 
— Structure  of  the  Rods  and  Matrix — Views  as  to  their  Nature  and 
Origin — Their  Mode  of  Arrangement- — The  Striae  of  Retzius — 
Views  as  to  their  Origin — The  Lines  of  Schreger — Enamel 
"Spindles" — Views  as  to  their  Origin  and  Nature — The  Amelo- 
dentinal  Boundary 

CHAPTER  IV 

Ortho-dentine 49 

Definition — Varieties — Origin — Gross  Anatomy — Structure  of  the 
Matrix — The  Tubes,  their  Measurements,  Curvatures,  Branches 
and  Contents — Views  as  to  the  Nature  of  the  Latter — The  Sheaths 
of  Neumann — Views  as  to  their  Nature — The  Interglobular  Spaces, 
Dimensions,  and  Contents — The  Granular  Layer  of  Tomes — The 
Lines  of  Schreger — The  Contour  Lines  of  Owen — Laminae — Views 
as  to  their  Nature — Secondary  Dentine 

xv 


XVI  CONTENTS 

CHAPTER  V 

PAGE 
The  Cementum  ..........................       79 

Definition  —  Origin  —  Distribution  —  Gross    Anatomy  —  Structure    of 
the  Matrix  —  Incremental  Lines  —  Perforating  Canals  and  Fibres 

CHAPTER  VI 

Structural  Modifications  of  the  Enamel,  Dentine,  and  Cementum  ....       93 
The  Enamel  of  the  Teeth  of  Rodents—  Of  the  Manatee—  Of  Fishes 

—  Tubular  Enamel  —  Views  as  to  its  Origin  and  Development  —  Plici- 
dentine  —  Vaso-dentine  —  Osteo-dentine  —  Classification  of  Dentines 

—  Lacunated  Cementum 

CHAPTER  VII 

The  Dental  Pulp   .........................     in 

Definition  —  Origin  —  Dimensions  —  Odontoblasts,  their  Shape,  Size, 
•  Relationships,  Structure,  Processes,  *  and  Analogies  —  Pulp  Cells 
Proper—  The  Stroma—  The  Basal  Layer  of  Weil—  The  Vascular 
System  —  Histology  of  the  Arteries,  Veins  and  Capillaries  —  The 
Nerve  Fibres,  their  Arrangement,  Structure,  and  Terminations  in 
Fishes,  Reptiles,  and  Mammals  —  Views  as  to  their  Ultimate 
Endings 

CHAPTER  VIII 

The  Alveolo-dental  Periosteum  ...................      166 

Definition  —  Origin  —  Dimensions  —  The      Fibrous      Elements  —  The 
Cellular  Elements  —  The  Blood  Supply  —  The  Nervous  System 


THE  ORAL  TISSUES 
CHAPTER  IX 

The  Oral  Cavity  and  its  Accessories  .................      181 

The  Minute  Anatomy  of  the  Lips  and  Cheeks  —  The  Tongue  —  The 
Salivary  Glands,  their  Ducts,  and  Mucous  and  Serous  Acini  —  The 
Hard  and  Soft  Palate—  The  Palatine  Tonsils 

CHAPTER  X 

The  Histology  of  the  Maxillary  and  Mandibular  Bones  .........     195 

Origin  —  Distribution  of  Varieties  of  Bone  —  General  Structure  of 
Bone  —  Structure  of  Bone  of  the  Canine  Fossa  —  Of  the  Interdental 
Septa—  Of  the  Hard  Palate—  Of  the  Wall  of  the  Maxillary  Sinus 
—  Of  the  Mandible  —  Of  the  Alveolar  Process 


CONTENTS  XV11 

CHAPTER  XI 

PAGE 

A^Group  of  Minor  Structures 209 

The  Histology  of  the  Absorbent  Organ — Of  the  Dental  Capsule — 
Of  the  Gum,  its  Mucous  and  Sub-mucous  Tissues — Of  the  Mucous 
Membrane  of  the  Maxillary  Sinus,  its  Epithelium,  Sub-mucous 
Tissues  and  Glands 


Ill 

THE  HISTOGENESIS  OF  THE  TEETH  OF  MAMMALS, 
FISHES  AND  REPTILES 

CHAPTER  XII 

ThejDevelopment  of  the  Teeth  in  Mammalia 231 

Earliest  Phases  of  Evolution — Changes  in  the  Ectoderm — Forma- 
tion of  the  Dental  Furrow — The  Primary  Epithelial  Inflection — 
Origin  of  the  Lip-furrow  and  Tooth-band — Views  as  to  Derivation — 
Changes  in  the  Mesoderm — Evolution  of  the  Enamel  Organ — The 
Metamorphoses  Occurring  in  and  around  the  Tooth  Germ  at  the 
Period  of  Formation  of  the  Dentine  Germ — Structure  of  the  Enamel 
Organ — Changes  in  the  Dentine  Papilla — Subsequent  Embryo- 
logical  Changes — Evolution  of  the  Permanent  Tooth  Germs — The 
Blood  Supply  of  the  Developing  Dental  Tissues — The  Origin  of  the 
Blood-vessels,  their  Arrangement,  Mode  of  Distribution,  and  the 
Areas  Governed  by  Them — Latest  Research  in  the  Vascular  Supply 
— Final  Stages  of  Dental  Evolution — Origin  of  the  Dental  Capsule 
— Histories  of  the  Various  Structures  Concerned  in  the  Development 
of  the  Teeth — Development  of  the  Enamel — Views  as  to  its  Nature 
— Development  and  Growth  of  the  Dentine  and  Cementum — Table 
Showing  Phases  of  Growth  of  the  Several  Parts  of  Tooth  Germs  in 
Human  Foetuses  at  Half  Term — Measurements  of  the  Same — - 
Histogenesis  of  Ovarian  Teratomatous  Teeth 

CHAPTER  XIII 

Development  of^the  Teeth  in  Pisces,  Reptilia  and  Batrachia 312 

The  Evolution  of  the  Teeth  in  the  Cod — In  the  Dog-fish — In  the 
Crocodile — In  the  Lizard — In  the  Snake — In  the  Newt 

Appendix 327 

Note  A. — On  the  Functions  of  the  Cells  of  the  Pulp — Note  B. — 
Physiological  (Lacunar)  Absorption  of  the  Alveolar  Processes  of 
the  Jaws  of  Man 


PART  I 

THE  DENTAL  TISSUES 


CHAPTER  I 
PROLEGOMENA 

To  write  a  book  is  to  build  a  house.  When  completed,  the 
chapters  are  the  rooms,  adroitly  planned  and  suitably  fur- 
nished with  pictures  of  interest.  From  the  windows,  the  eye 
surveys  many  well-known  fields  and  oft- trodden  paths;  but, 
beyond,  it  is  unable  to  pierce  the  problem  hills  of  uncertainty. 

All  literature  relating  to  the  theme  of  this  thesis  must,  per- 
force, have  its  foundation  stones  laid  on  the  classic  work  of 
Hunter,  Kolliker,  Owen,  Tomes.  It  is  impossible  and  unwise 
to  ignore  this  work.  In  this  manner  the  following  pages  are 
but  comparable  to  a  new  wing  of  the  house  of  Dental 
Anatomy,  which  these  investigators  have  progressively  and 
successfully  raised;  and  if,  from  the  windows,  some  instructive 
glimpses  of  the  surrounding  country  can  be  obtained,  and  a 
few  finger-posts  pointing  to  the  unknown,  though  by  no 
means  unknowable,  be  discovered  by  the  eye — aided  not  by 
telescope,  but  by  microscope, — then  the  author  will  rest 
content. 

That  a  treatise  which  deals  chiefly  with  descriptions  of  the 
minute  anatomy  and  pathology  of  the  teeth  and  associated 
parts  should  be  specially  required  may  be  questioned  by 
some.  Inasmuch,  however,  as  these  tissues,  by  reason  of  their 
unique  constitution,  differ  most  strikingly  from  other  spe- 
cialised organs,  such  as  the  eye,  the  nose,  the  larynx;  in- 
asmuch also,  as  general  histological  text-books  treat  somewhat 
sparingly,  and  sometimes  incorrectly,  of  this  subject,  the 
production  of  these  pages  has  seemed  to  the  author  perfectly 
justifiable,  nay  more,  almost  a  necessity  in  these  latter  times. 
"Cui  bono?"  was  once  a  frequent  question;  but  there  can  be 
only  few  (if  any)  who  would  to-day  care  to  diminish  rather 
than  to  increase  the  range  of  knowledge,  and  limit  the  speciality 
of  Dental  Surgery  to  mere  mechanical  manipulations. 

3 


4  THE    DENTAL    TISSUES 

Dr.  Otto  Walkhoff,  Professor  of  Conservative  Dentistry  in 
the  University  of  Munich,  in  an  introduction  to  his  "Normal 
Histology  of  the  Human  Teeth,"  1901,  declares: 

"The  special  study  of  the  Histology  of  the  Teeth  is  the 
binding  link  between  practical  dental  surgery  and  general 
surgery.  The  branch  of  learning  which  deals  with  this  sub- 
ject is  of  great  importance  for  the  practical  knowledge  of  the 
prospective  dental  surgeon.  He  learns  not  only  the  minute 
anatomy  of  the  parts,  but  also  the  mutual  relationships  of 
those  parts.  Those  dental  surgeons  who  have  had  experience 
in  making  and  examining  sections  of  teeth  are  able  to  treat 
carious  cavities  \vith  greater  knowledge,  and  to  appreciate 
and  understand  any  complications  that  may  arise,  and  there- 
fore take  more  appropriate  and  more  therapeutic  measures 
than  those  unaccustomed  to  the  science.  With  the  fuller 
education  of  dental  surgeons  in  this  study,  the  production  of 
false  pathological  and  other  statements  will  be  relegated  to 
the  past.  Thus  one  acquainted  with  the  structure  of  the  tissues 
could  never  claim  to  completely  cleanse  and  solidly  fill  the 
root-canals  of  teeth.  A  due  regard  to  the  Histology  of  the 
tissues  of  the  mouth  (as  well  as  its  Bacteriology) ,  and  the  most 
perfect  execution  of  mechanical  operations  form  the  ground- 
work of  the  conservative  dentistry  of  later  years." 

It  must  also  be  added,  as  has  been  expressed  in  another 
place,  that  the  practice  of  microscopical  work  imparts  to  the 
student  that  delicacy  of  touch  and  nicety  of  adjustment  of 
digital  dexterity  which  is  impossible  of  attainment  by  other 
means  and  methods. 

This  book,  then,  is  published  with  the  avowed  purpose 
of  drawing  the  attention  of  the  reader  to  the  essentials  of  a 
profoundly  fascinating  branch  of  science;  of  indicating  some 
difficult  and  apparently  irreconcilable  and  irresolvable  histo- 
logical  propositions;  of  attempting  to  elucidate,  illuminate 
and  complete  other  recondite  and  unfinished  studies;  and 
finally,  of  establishing  upon  a  permanent  and  convincing 
basis  many  accepted  postulates  and  uncontested  facts. 

Dental  Histology,  with  its  collaterals,  is  nearly,  but  not 
quite,  an  inductive  science.  Unfortunately,  it  is  by  no  means 


PROLEGOMENA  5 

an  exact  one,  although,  through  the  medium  of  new  methods 
of  research,  there  is  no  reason  why,  during  the  next  half- 
century,  it  should  not  become  so. 

The  science  and  art  peculiar  to  it  are  of  paramount  impor- 
tance alike  to  student,  pathologist  and  surgeon.  In  the  inter- 
pretation of  many  ordinary  and  extraordinary  phenomena 
connected  with  the  genesis  and  evolution  of  the  teeth;  in  the 
solution  of  certain  obscure  physiological  and  anatomical  and 
pathological  problems;  in  the  every-day  diagnosis  of  oral 
and  dental  disease;  in  short,  in  the  undoubted  assistance  it 
can  and  does  render  to  the  earnest  worker  in  the  art  of  Dental 
Surgery,  it  may  fairly  be  claimed  for  this  subject  that  to-day 
it  cannot  be  dismissed  without  recognition,  or  without  the 
bestowal  upon  its  varied  aspects  of  such  thoughts  and  labour 
and  research  as  they  deserve.  In  its  scope  and  aims  it  is 
certainly  ancillary  to  no  other  branch  of  learning. 

On  so  slender  a  scaffolding  it  would  seem  somewhat  difficult, 
if  not  well-nigh  impossible,  to  build  up  such  a  large  and 
diversified  collection  of  valuable  and  interesting  data;  never- 
theless, a  moment's  .reflection  will  soon  assure  the  reader  that 
this  framework  is  extensive  even  in  its  limitations. 

To  attempt  to  recall  and  record  the  History  of  Dental 
Histology  would  form  a  congenial  and  satisfactory  task. 
Mere  mention  of  the  names  of  those  specially  associated 
with  it  must,  however,  here  suffice.  As  for  the  past,  it  is 
pleasant  to  an  Englishman  to  dwell  on  the  works  of  Thomas 
Huxley,  Sir  Richard  Owen,  Salter,  Sir  John  Tomes,  Storer 
Bennett;  while  as  for  the  present,  the  bibliography  of  British 
dental  science  has  been  enriched  by  the  writings  of  C.  S. 
Tomes,  who  has  patiently  and  laboriously  investigated, 
among  other  subjects,  the  development  of  the  teeth  of  fishes, 
reptiles,  batrachians,  and  marsupial  mammals;  of  Howard 
Mummery,  to  whom  our  knowledge  of  the  development  and 
growth  of  dentine  is  largely  due;  of  Milles  and  Underwood, 
in  their  researches  on  dental  caries;  of  Leon  Williams,  the 
able  and  skilful  exponent  of  the  structure  and  pathology  of 
human  enamel;  of  Paul,  who  has  successfully  demonstrated 
the  minute  anatomy  of  Nasmyth's  membrane;  of  J.  G. 


6  THE   DENTAL   TISSUES 

Turner,  who  has  identified  himself  with  the  etiology  and  pa- 
thology of  dental  cysts;  and  of  Kenneth  Goadby,  the  prolific 
contributor  to  current  literature  of  a  mass  of  information 
on  dental  and  oral  mycetology,  etc.  In  America,  the  list  of 
names  must  be  headed  by  those  of  Andrews,  Black,  Norman 
Broomell,  etc.;  and  on  the  Continent  of  Europe  by  those  of 
Arkovy,  von  Ebner,  Galippe,  Grevers,  Kolliker,  Legros,  Magi- 
tot,  Miller,  Retzius,  Rose,  Vignal,  Walkhoff,  Wedl,  Weil, 
Zsigmondy,  etc. 

Rising  out  of  a  review  of  this  subject  come  many  thoughts, 
and  chief  among  them  are  the  remarkable  scantiness  of  actual 
and  reliable  information  concerning  many  things.  Thus,  with 
regard  to  the  normal  minute  anatomy  of  the  hard  tissues,  no 
answers  have  been  returned  to  the  questions,  "How  is  enamel 
fixed  so  intimately  to  the  periphery  of  the  dentine?"  "Whence 
comes  its  pigmentation?"  "What  is  the  manner  of  develop- 
ment of  the  branches  of  the  dentinal  tubes?"  As  to  the  pulp 
and  alveolo-dental  periosteum,  some  knowledge  is  available 
of  the  nerve  endings  in  the  first,  while  the  histology  of  the 
latter  still  remains,  as  far  as  its  nervous  system  is  concerned, 
a  terra  incognita, 

Turning  to  the  realm  of  Pathology  in  general,  and  erosion 
of  the  teeth  in  particular,  the  causes  of  the  occurrence  of  occlu- 
sion of  the  tubes  requires  further  consideration,  as  do  also  the 
presence  and  sensitiveness  or  non-sensitiveness  of  the  inter- 
globular  spaces  in  hypoplasic  teeth  and  ovarian  cystic  teeth, 
the  changes  in  the  dentinal  tubes  producing  the  "pipe-stem" 
appearance  of  caries,  and  their  invisibility  in  senile  affections. 
Tempting  fields  for  research  are  all  these  and  many  others. 
The  exigencies  of  this  chapter  disallow  more  than  the  brief 
consideration  of  one  subject  for  discussion — viz.,  the  pig- 
mentation of  enamel. 

Thick  sections  of  this  tissue  examined  macroscopically  before 
finally  grinding,  polishing  and  mounting  always  appear  stained 

more  or  less  deep  brown  colour.  This  is  different  from  and 
other  than  that  of  the  brown  striae  of  Retzius.  The  thinnest 
sections  ultimately  reveal  apparently  but  little,  if  any,  pig- 
mentation. Is  this  colouring,  then,  due  to  mere  optical  effects? 


PROLEGOMENA  7 

In  the  opinion  of  the  author,  No.  Because,  examples  of  the 
natural  staining  of  epithelial  tissues  constantly  occur — as  in 
the  case  of  the  epidermis  of  the  negro,  where  granules  of 
melanin  are  found  in  the  rete  Malpighii  of  the  epithelial  layer 
of  cells.  Other  analogies  may  be  cited  also — e.g.,  the  pigment 
corpuscles  in  the  ramified  nerve  cells  in  the  anterior  cornua 
of  the  spinal  cord  of  man,  and  the  pigment  bodies  in  the  cortical 
substance  of  the  hairs  of  man. 

Again,  the  normal  pigmentation  of  the  enamel  is  a  prominent 
feature  of  the  teeth  of  many  rodents.  This  also  disappears 
on  grinding  very  thin;  and  it  is  impossible  to  say  whether  it 
is  resident  in  the  enamel  rods,  or  in  the  cementing  substance, 
or  in  both.  The  tissue  is  unequally  pigmented;  if  it  was  due 
to  the  chromatic  aberrations  of  light  it  would  most  likely  be 
uniform.  Finally,  in  the  case  of  pathological  or  congenital 
pigmentation  of  the  cementum  and  dentine,  the  colour,  though 
pronounced  in  thick  sections  or  even  before  these  have  been 
made,  has  vanished  when  the  thinnest  are  examined.  The 
inference  would  be  that  this  may  also  hold  good  with  regard 
to  enamel. 

It  would  seem  that  the  dental  histologist  of  the  future  must 
more  closely  combine  microscopical  technics  with  a  profounder 
knowledge  of  anatomy  and  physiology. 

Of  the  utmost  importance  to  such  an  one  are  three  great 
principles, — the  selection  of  material,  the  preparation  of  that 
material  for  experimental  and  histological  research,  and  the 
correct  interpretation  of  results. 

First,  the  selection  of  material  which  is  about  to  form  the 
basis  of  investigation  must  not  only  be  confined  to  perfectly 
fresh  tissues,  but  as  far  as  it  is  possible  to  determine  to  tissues 
absolutely  unaffected  by  morbid  conditions.  This  may  be 
exemplified  by  the  study,  say,  of  the  histogenesis  of  the  teeth 
in  normal  well-developed  embryos  and  foetuses  as  compared 
with  the  different  stages  and  rates  of  growth  in  rachitic  indi- 
viduals of  a  corresponding  age.  Contrasting  the  appearance 
of  the  two  conditions  may  throw  useful  light  on  both;  but 
conclusions  drawn  from  examination  of  diseased  tissues  errone- 
ously believed  to  be  healthy,  can  only  give  rise  to  false  deduc- 


8  THE    DENTAL    TISSUES 

tions  and  misleading  statements.  Loose  plans  of  procedure 
unfortunately  militate  strongly  against  that  advancement  of  the 
science  which  is  so  earnestly  desired. 

Further,  the  preparation  of  the  tissues  is  all  important. 
The  quotation  of  one  single  instance,  in  itself  sufficiently 
striking,  will  be  enough.  The  discovery  of  the  real  nature 
and  characteristics  of  Nasmyth's  membrane  has  followed  the 
employment  of  proper  methods  of  preparation. 

Thirdly,  tissues  having  been  properly  selected  and  prepared, 
suitably  stained  and  carefully  mounted — the  risk  of  shrinkage 
or  swelling  having  been  reduced  to  a  minimum — must  be 
scrutinizingly  examined  and  carefully  and  critically  inter- 
preted. It  was  undoubtedly  the  precipitation  of  amorphous 
silver  chromate  salts  (as  in  Golgi's  method  of  staining)  or 
methylene-blue  granules  which  lead  Morgenstern  and  Romer 
to  erroneously  affirm  the  actual  presence  of  amyelinic  nerve 
fibres  in  the  dentinal  tubules  and  enamel.  Check  experiments 
must  be  conscientiously  followed,  and  check  stainings  and 
methods  of  preparation  adopted. 

In  conclusion,  the  original  worker  must  be  assisted  in  his 
accurate  explanations  of  the  meanings  of  the  structures  of 
cells  and  organs  by  keeping  himself  quite  en  rapport  with  the 
latest  teachings  of  physiology  and  pathology.  He  will  be  most 
helped  by  devoting  his  attention  to  a  preliminary  thorough 
study  of  the  knowledge  we  possess  of  the  differentiated  func- 
tions of  cells;  of  the  general  principles  that  underlie  and 
govern  the  physiological  methods  of  tissue  formation;  of  the 
metabolism  of  the  cells  forming  the  component  parts  of  that 
tissue;  and  of  the  effects  of  pathological  influences  on  the  life- 
histories  of  the  cells  and  other  essential  elements  of  the  organs 
with  which  he  has  to  deal. 


CHAPTER  II 
NASMYTH'S  MEMBRANE 

MICROSCOPICAL  ELEMENTS:  (i)   Cellular  layer;  (ii)  Translucent  pellicle 
GENERAL   CHARACTERISTICS 

Definition.- — A  macroscopically-invisible  cellule-laminar  film 
situated  on  the  free  surface  of  the  adult  enamel  of  man  and 
certain  animals. 

Origin. — This  tissue,  which  has  recently  been  studied  afresh 
microscopically,  is  now  known  to  have  its  origin  as  an 
ectodermic  formation  of  the  epithelial  cells  of  the  enamel  organ. 

It  is  most  probable  that  the  cellular  layer  is  derived  from 
the  external  epithelium,  and  the  pellicle  or  innermost  layer 
from  the  spent  cells  of  the  internal  epithelium,  which  have 
previously  undergone  a  keratinous  or  somewhat  analogous 
change. 

With  regard  to  its  origin,  R.  R.  Andrews  (''The  American 
Text-book  of  Operative  Dentistry/'  p.  92,  1901),  says  that  his 
investigations  lead  him  to  believe  that  the  internal  epithelium 
of  the  enamel-organ  (ameloblasts)  composes  the  cells  of  the 
membrane.  These  "having  performed  their  function,  have 
filled  with  calcoglobulin  and  have  partially  calcified,  becoming 
somewhat  like  that  tissue  which  we  find  on  the  borderland  of 
calcification."  That  this  is  an  entirely  incorrect  view  is 
obvious  when  Paul's  and  the  author's  sections  are  examined. 

Distribution. — Situated  externally  on  the  cortical  aspect  of 
the  unworn  enamel  of  man,  monkey  and  sheep,  is  found  under 
suitable  conditions  Nasmyth's  membrane.  It  is  a  thin  con- 
tinuous tissue  spread  flat  over  the  enamel,  dipping  into  the 
naturally-formed  pits  and  fissures  on  the  surface,  and  limited 
in  extent  by  the  cervical  portion  of  the  tooth,  to  the  edges  of 

9 


10  THE    DENTAL    TISSUES 

which  it  is  attached.  Synonym.- — The  enamel  cuticle.  It  has 
also  been  incorrectly  termed  "persistent  dental  capsule." 

Bodecker1  considers  that  it  is  in  direct  union  with  the  outer- 
most epithelial  layer  of  the  gum,  being  therefore  the  only 
layer  which  closes  up  the  space  between  the  neck  of  the  tooth 
and  the  adjacent  gum. 

In  a  well-developed  adult  premolar  its  measurements  are 
29  mm.  in  its  widest  part,  19  mm.  in  the  narrowest,  and  26  mm. 
round  the  cervical  region  of  the  tooth.  All  teeth  possess  the 

E 


C 


FIG.  i. —  Nasmyth's  membrane  attached  to  the  cementum.  Prepared  by 
decalcification  of  a  ground  section.  Magnified  40  times,  p.  The  membrane; 
E.  Enamel;  D.  Dentine;  c.  Cementum. 

membrane  in  a  more  or  less  complete  condition.  Even  senile 
teeth  when  treated  with  a  decalcifying  solution  to  remove 
the  enamel  have  traces  of  it,  but  it  is  best  observed  in  those 
teeth  which,  while  still  unerupted  (premolars,  for  instance), 
have  been  removed  for  the  treatment  of  irregularities,  because 
in  this  case  the  cellular  layer  is  undamaged,  though  it  may 
be  injured  during  the  act  of  extraction.  Portions  of  the 
cellular  layer  may  remain  attached  to  the  inner  aspect  of  the 

1  "Anatomy  and  Pathology  of  the  Teeth,"  p.  43,  1894. 


NASMYTH  S    MEMBRANE  II 

dental  capsule,  which  as  a  rule  comes  away  with  the  tooth. 
According  to  Kolliker  it  measures  in  thickness  from  i/u  to  2/j.. 
This  is  probably  erroneous,  a  measurement  of  50^  being  likely 
to  be  more  accurate.  Easily  detached  by  the  action  of  strong 
acids,  it  is  only  when  Paul's  method  of  preparing  specimens  is 
adopted  that  its  real  normal  structure  is  ascertained. 

HISTOLOGY 

Nasmyth's  membrane  consists  of  two  parts  (i)  an  outer 
cellular  portion,  and  (ii)  an  inner  structureless  translucent 
lamina  or  pellicle.  These  are  both  intimately  adherent,  not 
only  to  each  other,  but  also  to  the  free  ends  of  the  underlying 
enamel  columns. 

(i)  The  Cells 

The  cellular  portion  is  interesting,  inasmuch  as  its  structure 
is  made  up  of  a  layer  or  layers  of  large  polygonal  flattened 
epithelial  cells,  with  pronounced  nuclei.  "The  epithelial  cells," 
writes  Bodecker  (op.  cit.  p.  92),  "in  transverse  section,  have  the 
appearance  of  shallow  spindles.  Not  infrequently  there  occurs 
also  a  stratified  epithelium  on  the  surface  of  the  tooth.  The 
enamel-fibres  are  in  connection  with  these  epithelial  bodies 
which,  if  detached,  show  delicate  offshoots  adhering  in  regular 
intervals — the  broken  enamel  fibres.  Sometimes  the  surface 
of  the  enamel  is  coated  by  a  thin  uniform  layer  of  protoplasm 
with  regularly  scattered  nuclei.  In  such  an  instance  single 
epithelia  are  not  traceable,  though  scarcely  any  doubt  can  arise 
about  the  epithelial  nature  of  this  layer." 

It  is  quite  possible  and  most  probable  that  the  cells  are 
more  than  one  layer  in  depth.  Preparations  when  correctly 
stained  exhibit  such  a  dense  pattern  of  cells  that  this  belief 
in  the  multiplicity  of  layers  is  probably  well  founded.  It  is 
doubtful,  however,  if  more  than  three  layers  ever  exist.  The 
double  or  treble  layers  are  not  observed  all  over  the  surface 
of  the  pellicle,  but  only  in  those  situations  where  the  membrane 
dips  down  deeply  into  the  pits  or  crevices  of  the  enamel;  and 
here  too  the  pellicle  itself  is  apparently  thicker  than  elsewhere. 
The  protoplasm  of  the  cells  is  faintly  granular.  Under  high 


12 


THE    DENTAL    TISSUES 


powers,    the   spongioplasm   and   hyaloplasm   may   be   clearly 
defined.1 


FIG.  2. — A  piece  of  the  thinnest  portion  of  Nasmyth's  membrane  flattened 
out,  and  photographed  from  above.  Its  elastic  nature  made  it  impossible  to 
critically  focus  it  in  all  parts.  Prepared  by  Paul's  method.  Magnified  200 
times,  c.  Nuclei  of  the  cells;  p.  Translucent  pellicle. 

1  The  "spongioplasm,"  according  to  Schafer,  is  a  reticulum  or  network  of 
protoplasm  in  the  cell  substance;  and  "hyaloplasm"  is  the  name  applied  to  the 
material  which  occupies  or  fills  its  meshes. 


NASMYTH  S    MEMBRANE  13 

Paul1  attributes  to  the  cells  an  average  diameter  of  i2/z  and 
a  length  of  25^1.  Cells  having  "cogged"  outlines — spiny- 
cells — are  seen  constantly  (Cf.  Fig.  196) :  and  in  places  the 
polygonal  cells  are  flattened,  probably  by  mutual  pressure,  in 
one  or  more  lateral  directions,  and  may  thus  assume  a  cubical 
or  even  cylindrical  shape.  The  nuclei  are  particularly  large 
compared  to  the  size  of  each  cell,  are  ovoid  in  shape  or  nearly 
round  in  outline,  and  possess  faint  nucleoli.  These  are  usually 
single,  and  often  contain  in  their  interiors,  as  well  as  near  their 
exteriors,  one  or  more  vacuole-like,  bright,  shining  globules. 

(ii)   The  Pellicle 

The  inner  or  subepithelial  layer  is  a  delicate  continuous 
membrane,  apparently  without  histological  structure  of  any 
kind.  It  is  translucent,  elastic  and  cornified,  and  resists  the 
action  of  acids  in  a  similar  way  to  the  sheaths  of  Neumann 
or  the  linings  of  Haversian  canals.  On  its  under  surface,  i.e., 
the  part  nearest  enamel,  a  reticulated  pattern  can  be  fairly 
easily  demonstrated.  This  corresponds  to  and  is  probably 
produced  by  the  free  ends  of  the  enamel  rods,  which  have 
left  their  hexagonal  impressions  on  the  membrane.  It  is  to 
be  noted  that  the  hexagons  of  the  pattern  have  sharp,  clear 
margins  made  up  of  straight  outlines,  correspond  in  size  to 
the  diameter  of  the  enamel  rods,  and  in  no  way  approximate 
the  size  of  the  epithelial  cells  which  are  "at  least  ten  times 
too  large  for  the  enamel  rods."  (Paul.) 

In  sections  of  Xasmyth's  membrane  which  have  been 
obtained  in  situ  it  has  been  possible  to  find  in  the  deep  enamel- 
pits  lacunae  similar  to  those  of  osseous  tissue,  surrounded  by  a 
capsule,  and  apparently  associated  very  closely  with  the  trans- 
lucent layer  of  the  membrane.  Tomes2  has  repeatedly  seen 
this  condition.  How  these  encapsuled  cells  get  into  the  pits 
or  fissures  is  not  quite  clear.  There  is  an  occasional  appear- 
ance noticed  in  teased  or  spread-out  pieces  of  the  membrane 
of  the  cells  being  arranged  concentrically  round  certain  tiny 
spaces,  and  it  may  be  that  these  represent  in  some  way  the 

1  "Nasmyth's  Membrane."     The  Dental  Record,  1894. 
2  "A  Manual  of  Dental  Anatomy,"  p.  123,  1914. 


THE   DENTAL   TISSUES 


spots  where  encapsuled  lacunae  may  be  deposited.  A  lacuna 
may  perhaps  represent  a  persistent  retained  and  imprisoned 
cell  of  the  stratum  intermedium  of  the  enamel  organ  where, 
owing  to  the  formation  of  the  cusps  of  the  teeth,  an  involution 


FIG.  3. — A  thicker  portion  of   Nasmyth's  membrane  than  in  Fig.   2.      Magni- 
fied 200  times.     A.  Hexagonal  impressions  of  the  enamel  rods. 

of  this  layer  of  cells  has  taken  place;  or  it  may  represent  an 
aberrant  osteoblast  which  has  likewise  remained  unatrophied 
or  unabsorbed. 

Prof.  Rodolfo  Erausquin  of  the  University  of  Buenos  Aires, 
in  a  private  letter  to  the  author,  expresses  the  opinion  which  is 
very  plausible,  that  the  so-called  "encapsuled  lacunae"  are, 
after  all,  merely  vegetable  cells  introduced  into  the  deep  pits  of 


NASMYTH'S  MEMBRANE 


M 


FIG.  4.— Enamel  of  a  tooth,  with  Nasmyth's  membrane  on  the  free  surface, 
removed  from  an  oophoronic  cyst  or  teratoma.  Ground  thin  and  then  decal- 
cified. Unstained.  Magnified  250  times.  M.  Nasmyth's  membrane. 


FIG.   5. — Vegetable  cells  found  in  a  pit  on  the  surface  of  human  Nasmyth's 
membrane.      Photomicrograph  supplied  by  Dr.  R.  Erausquin. 


1 6  THE   DENTAL   TISSUES 

enamel  during  the  act  of  comminution  of  food,  where  they  may 
be  retained  indefinitely.  The  accompanying  photomicrograph 
adequately  represents  the  microscopical  appearances  of  such 
cells. 

Fresh  research  on  this  matter  is  needed  before  a  dogmatic 
opinion  can  be  expressed. 

It  is  now  perfectly  established  that  Nasmyth's  membrane 
can  be  regarded  with  certainty  as  an  epithelial  remnant  of 
the  enamel  organ,  and  thus  the  theories  of  Waldeyer,  Rose, 
and  others  are  to  be  considered  correct. 

From  the  enamel  of  recent  teeth  removed  from  ovarian 
teratomatous  cysts,  the  pellicle  can  be  isolated  by  careful 
decalcification. 

It  is  absent,  from  the  crowns  of  teeth  found  in  follicular 
odontomes  (q.v.),  although,  according  to  Warwick  James, 
("The  Science  and  Practice  of  Dental  Surgery,"  edited  by 
Xorman  G.  Bennett,  1914)  this  is  not  always  the  case. 


CHAPTER  III 

THE  ENAMEL 

MICROSCOPICAL  ELEMENTS:  (i)  Enamel  rods  and  intercolumnar  sub- 
stance; (ii)  Curvatures  of  rods;  (iii)  Brown  Striae  of  Retzius;  (iv) 
Lines  of  Schreger;  (v)  Enamel  "Spindles." 

GENERAL  CHARACTERISTICS 

Definition. — The  smooth,  hard,  glistening  inorganic  sub- 
stance which  partially  or  wholly  envelopes  the  crowns  or  visible 
portions  of  the  calcined  teeth  of  the  Pisces,  Reptilia,  and  Mam- 
malia classes  of  the  Vertebrata. 

Origin. — It  is  the  final  product  of  the  layer  of  cells — the 
ameloblasts — which  constitute  the  internal  epithelium  of  the 
enamel  organ.  It  is  yet  undecided  whether  enamel  is  a  secretion 
or  conversion  of  these  cells,  but  the  balance  of  opinion  would 
seem  to  be  in  favour  of  the  former. 

Distribution. — Existing  as  (i)  a  tiny  point  or  tip,  as  in  the 
teeth  of  some  members  of  the  class  Pisces,  e.g.,  the  order  Ana- 
canthini- — Merlucius  vulgaris  (the  hake),  the  order  Physos- 
tomi,  family  Muraenidae — Anguilla  acutirostris  (the  eel); 
or  (ii)  a  partial  investment  of  the  cutting  edges  of  teeth,  such 
as  those  of  the  incisors  of  Rodentia,  the  lower  canines  of  some 
Bunodonts,  &c.;  or  (iii)  longitudinal  bands,  as  in  the  upper 
canines  (tusks)  of  the  wild  boar ;  or  (iv)  an  entire  cap  of  varying 
thickness,  which  covers  over  the  normally  erupted  parts  of  the 
teeth  of  mammalia  generally,- — except  of  the  sub-order  Artio- 
dactyla,  where  a  thick  coating  of  cementum  is  developed 
in  this  situation, — enamel  is  the  hardest  tissue  of  the  teeth 
or  any  of  the  organs  of  man  and  animals.1 

1  In  the  mandibular  incisors  of  the  Chiromydcc  (e.g.,  the  Aye  Aye)  enamel 
forms  by  far  the  greater  portion  of  the  teeth,  exceeding  in  amount  both  dentine 
and  cementum. 

2  17 


i8 


THE    DENTAL    TISSUES 


In  man  it  intervenes  between  the  translucent  pellicle  of 
Nasmyth's  membrane,  placed  externally,  and  the  periphery 
of  the  dentine  which  goes  to  make  up  the  greater  part  of  the 
tooth  substance  internally.  Nasmyth's  membrane  is  invisible 
macroscopically;  at  least  it  is  unrecognisable,  and,  therefore, 
as  this  film  becomes  abraded  the  enamel  becomes  the  most 
external  of  the  dental  tissues. 

In  the  Artiodactyla  it  occupies  a  position  (Fig.  6)  between 
the  cementum  and  the  dentine. 


FIG.  6. — Vertical  section  of  a  molar  of  a  young  horse.     Section  ground  thin. 
Unstained.      Magnified  45  times.      E.  Enamel;  D.  Dentine;  c.  Cementum. 

In  sagittal  (vertical  labio-lingual)  sections  of  the  well- 
developed  incisor  teeth  of  man.  unworn  by  attrition,  it  measures 
at  the  incisive  edge  about  2  mm.  in  depth;  and  then,  as  it 
gradually  approaches  the  cervical  margin,  it  becomes  thinned 
down  to  zero.  Over  the  cusps  of  premolars  it  is  2.3  mm.,  and 
over  the  cusps  of  molars  it  is  2.6  mm.  in  thickness. 

The  enamel  of  the  deciduous  teeth  may  be  half  the  thickness 
of  that  of  the  permanent  series. 

At  the  gingival  edge  it  may  or  may  not  slightly  overlap  the 


THE    ENAMEL 


thin  structureless  border  of  cementum.  Monsieur  Jules 
Choquet,  who  investigated  (1899)  the  question  of  the  anatom- 
ical relationships  of  the  two  tissues,  in  an  interesting  brochure 


FIG.  7. 


FIG.  9. 


FIG.   10. 


FIGS.  7,  8,  9,  and  10. — Adapted  from  photomicrographs  by  Jules  Choquet, 
and  published  by  L'Odontologie,  1899.  Semi-diagrammatic.  Human.  H. 
Enamel;  c.  Cementum;  D.  Dentine. 

entitled  "Note  sur  les  rapports  anatomiques  existant  chez 
rhomme  entre  1'email  et  le  cement,"  has  succeeded  in  throw- 
ing light  on  this  subject.  He  examined  and  reported  on 
twenty-nine  human  teeth;  and  found  that  the  enamel  covered 


2O 


THE    DENTAL   TISSUES 


the  edge  of  cementum  eight  times  (Fig.  9),  while  the  cementum 
overlapped  the  enamel  seven  times  (Fig.  8).  This  author  also 
reports  that,  in  the  majority  of  cases,  the  enamel  and  cementum 
meet  each  other,  and  there  is  no  overlapping  (Fig.  7).  Out  of 
his  twenty-nine  sections  this  occurred  nineteen  times.  Thus 
the  rule  would  be  that  the  two  tissues  are  in  absolute  contact, 
and  both  lie  in  the  same  plane  without  any  involution  what- 
soever. Choquet  further  found  that  in  27.5  per  cent,  of  the 
cases  he  examined,  there  was  a  breach  of  continuity  of  these 
two  structures,  leaving  a  minute  portion  of  the  dentine  fully 
exposed  (Fig.  10).  His  sections  were  cut  longitudinally, 


FIG.   it. — Vertical  section  of  a  Human  tooth,  from  a  photomicrograph.     Semi- 
diagrammatic.      E.  Enamel;  D.  Dentine;  c.  Cementum. 

and  some  were  studied  on  both  their  aspects,  whilst  others 
only  on  one.  "Cette  difference  tient  a  ce  que  dans  certains 
cas  il  y  avait  eu  fracture  de  1'email  d'un  des  bords  pendant 
1'usure  de  la  coupe."  There  was  often  a  diversity  of  method 
of  ending  of  the  tissues:  thus,  one  section  would  have  on  its 
labial  aspect  the  enamel  overlapping  the  cementum,  and  on  its 
lingual  surf  ace,  the  former  internal  to  the  latter.  The  teeth  were 
representative  specimens  from  young,  old,  and  gouty  subjects. 
This  subject  has  been  re-examined  by  Thorsen  (Den  Norske 
Tandlaege  Tidende,  1917,)  who  finds  that  enamel  meets 
cementum  edge  to  edge  in  30  per  cent,  of  cases;  is  covered  by 
cementum  in  60  to  65  per  cent.,  and  covers  cementum  in  0.5 


THE    ENAMEL  21 

per  cent.  In  5  to  10  per  cent,  the  two  tissues  were  not  in 
contact. 

On  rare  occasions,  as  in  Fig.  n,  from  a  section  in  the  pos- 
session of  Sydney  Spokes,  the  margin  of  cementum  may  extend 
in  a  remarkable  way,  some  considerable  distance  over  the  edge 
of  enamel.  From  the  structure  of  the  tissue,  consisting  as  it 
did  of  matrix  containing  many  large  lacunas  and  incremental 
lines,  it  is  important  to  point  out  the  fact  that  the  cementum 
was  in  no  sense  normal.  The  tooth,  a  mandibular  third  molar, 
was  slowly  erupting  in  an  irregular  manner. 

Macroscopical  Appearances. — Surface  smooth,  shiny,  some- 
times traversed  by  tiny  vertical  or  horizontal  depressions, 
occasionally  scrobiculated  and  normally  deeply  fissured  in 
premolars  and  molars,  and  pure  white  in  colour.  When 
fractured,  pure  white,  non-lustrous. 

HISTOLOGY 

On  microscopical  examination  Human  enamel  reveals  many 
interesting  structures.  These  may  be  described  in  the  order 
of  their  importance  as:  (i)  The  striated  columns  and  calcified 
matrix;  (ii)  The  curvatures  or  courses  of  the  rods;  (iii)  The 
brown  stria?  of  Retzius;  (iv)  The  lines  of  Schreger;  and,  (v) 
Certain  spaces  or  "enamel  spindles." 

(i)  Enamel  Rods  (Alan) 

Enamel  is  built  up  of  minute  solid  calcified  columns  or  rods, 
frequently  hexagonal  or  pentagonal  in  shape,  all  united  by  a 
matrix  or  intercolumnar  cementing  material  of  somewhat 
different  refractive  index.1  It  is  probable  that  the  real  shape 

*It  is  extremely  difficult  to  estimate  the  chemical  composition  of  enamel. 
Hoppe-Seyler  (Handbuch  d.  Physiolog.  und  Pathologisch-chem.  Analyse,  1893) 
has  the  following  formula:  Cai0CO3  (POO 6,  95-35  per  cent.;  MgHPO4.  1.05 
per  cent,  and  so-called  "organic  substance,"  3.60  per  cent.;  while  Dr.  Lovatt 
Evans  (Proc.  Internal.  Med.  Congress,  1913)  thinks  that  in  dried  enamel  of 
man  the  organic  material  amounts  to  i  per  cent,  or  2  per  cent.,  for  he  com- 
puted that  3.659  gm.  contained  39.56  c.c.  of  gas  consisting  of  carbon  dioxide 
30.21  c.c.,  and  nitrogen  9.35  c.c. 

The  "organic  substance,"  and  "organic  material"  mentioned  above  are 
probably,  as  Tomes  has  shown,  (Dental  Anatomy,  1914,  p.  34),  only  water  com- 
bined with  the  lime  salts. 


22 


THE    DENTAL   TISSUES 


of  the  columns  is  that  of  a  solid  cylinder.     If  an  ameloblast 
could  undergo  complete  segregation  and  continue  its  functional 


FIG.  12. — Sagittal  section  of  the  incisive  edge  of  a  Human  incisor  tooth. 
Ground  thin.  Unstained.  -  Magnified  45  times.  Shows  the  general  pigmented 
appearance  of  the  enamel.  E,  Enamel;  D.  Dentine. 

activity  a  rounded  rod  would,  no  doubt,  result.     The  hexagons 
are  most  likely  produced  by  the  lateral  pressure  of  lengths  of 


THE    ENAMEL 


23 


contiguous   rods,   in   much   the  same  way  as   obtains  in   the 
six-sided  cells  of  the  bee's  honey-comb   (See  Fig.   15).     The 


FIG.   13. — Sagittal  section  of  the  incisive  edge  of  a  Human  canine  tooth.      Ground 
thin.      Unstained.      Magnified  45  times.      E.  Enamel;  D.  Dentine. 

matrix  is  not  a  connective  tissue  ground  substance;  but  merely 
a  more  or  less  perfectly  calcified  cementing  substance. 


THE    DENTAL    TISSUES 


/ 

^ 


FIG.   14  — Human     enamel.     Prepared     by     grinding.      Unstained.      Magnified 

250  times. 


FIG.  15. — Enamel  rods,  as  seen  in  transverse  section.     Decalcified  and  teased 
out.      Magnified  500  times. 


THE    ENAMEL  25 

When  isolated  by  means  of  the  careful  application  of  dilute 
acid  solutions,  the  rods  have  their  cementing  substance  dis- 
solved and  can  then  be  examined  critically  (Fig.  16).  They  are 
absolutely  solid  in  the  adult  or  mature  state,  i.e.,  when  fully 
completed,  rather  flexuous  or  curved  in  contour,  and  measure 
.005  mm.  (5/x)  in  diameter.  Kolliker  in  "A  Manual  of  Human 
Microscopic  Anatomy,"  1860,  gives  their  breadth  as  6.4^  to 
5-iju.  Their  length  may  attain  to  2  mm.  The  outlines  of 


FIG.    16. — Transverse  section  of  enamel  rods,  magnified  2,000  times. 
Photomicrograph  by  Leon  Williams. 


the  rods,  in  addition  to  being  curved,  are  beaded,  or  very 
slightly  varicose.  Their  long  axes  are,  speaking  broadly,  placed 
at  right  angles  to  the  surface  of  the  tooth.  Their  inner  ex- 
tremities are  inserted  securely  in  tiny  hexagonal  depressions 
on  the  surface  of  the  dentine:  while  their  outer  ends  are  free, 
and  crop  out  of  the  periphery  of  the  enamel  itself,  thus  giving 
rise  to  imbrication  lines  on  its  cortical  outer  aspect,  and  probably 
affording  close  attachment  to  the  pellicle  of  the  enamel  cuticle, 
to  the  hexagonal  impressions  of  which  they  are  ultimately  and 
intimately  fixed  (see  Fig.  3). 


26 


THE    DENTAL    TISSUES 


The ''term  "imbrication  lines"  has  been  introduced  by  Prof. 
Pickerill  of  the  University  of  Otago,  New  Zealand,  ("The  Pre- 
vention of  Dental  Caries  and  Oral  Sepsis,"  1912),  to  describe 
these  outcrops  on  the  surface  of  enamel  of  the  free  ends  of 
the  rods.  He  has  clearly  demonstrated  the  fact  that,  to  a 
slight  extent,  the  ridges  and  furrows  of  the  enamel  periphery 


FIG.  17.- — Section  of  enamel  from  Human  tooth.  Magnified  2,000  times. 
Dark  ground  illumination.  Focussed  in  the  middle  of  the  section  to  show  the 
granular  calcified  plasm-strings.  The  transparency  of  the  cement-substance 
between  the  enamel  rods  is  perfectly  demonstrated  in  this  illustration.  Photo- 
micrograph by  Leon  Williams. 

are  made  up  of  the  overlapping  free  terminations  of  the  rods. 
Inasmuch  as  this  arrangement  resembles  that  which  obtains 
generally  in  the  disposition  of  the  scales  of  a  fish,  or  the  tiles  of 
a  house  roof,  the  term  is  very  appropriate. 

At  regular  linear  intervals,  and  at  distances  varying  from 
5iu  to  3-5/i,  the  enamel  rods  are  crossed  by  distinct  shadings 


THE   ENAMEL  27 

called  transverse  striae  or  varicosities,  which  closely  resemble 
the  stripes  of  striated  voluntary  muscle  fibres  (Figs.  18  and  23). 
These  striae  are  only  seen  in  longitudinal  or  oblique  sections 
of  the  rods,  and  are  ordinarily  very  faint.  They  are  rendered 
more  apparent  by  the  action  of  dilute  hydrochloric  acid,  and 


FIG.  1 8. — Section  of  enamel  from  Human  tooth.  Magnified  350  times. 
Section  prepared  by  Howard  Mummery.  The  transverse  markings  of  the 
enamel-rods  are  very  pronounced.  The  enamel-rods  are  everywhere  seen  to  be 
united  by  projecting  processes.  Photomicrograph  by  Leon  Williams. 

occasionally  when  a  H  per  cent,  solution  of  chromic  acid  has 
been  used.  The  markings  are  more  clearly  and  easily  seen  in 
the  outer  portions  of  the  enamel,  and  may  be  remarkably 
demonstrated  in  very  pigmented  or  degenerated  conditions  of 
the  hard  tissues:  they  may  be  very  indistinct,  or  even  absent, 
in  the  region  of  the  enamel  near  the  dentine. 


28 


THE    DENTAL    TISSUES 


According  to  Bodecker  the  enamel  is  traversed  by  fibres  of 
living  matter  located  in  the  interstices  between  the  enamel  rods. 
The  fibres  are  connected  with  one  another  by  delicate  fibrillae, 
piercing  the  enamel  rods  in  a  vertical  direction.  Besides  these 
rectangular  unions,  the  basis-substance  contains  a  minute  net- 
work of  living  material  which  pervades  it  throughout  its  whole 
extent.  The  enamel  fibres  send  conical  thorns  toward  the 


ER 


E  F 


E  R 


D  F 


FIG.  19. 


FIG.  20. 


FIG.  19. — Transverse  section  of  enamel,  after  Bodecker.  Magnified  2,000 
times.  E.R.  Rods  of  enamel,  partly  exhibiting  formations  like  nuclei;  the  light 
interstices  between  the  rods  traversed  by  delicate  beaded  fibres;  E.F.  or  by 
vertical  thorns. 

FIG.  20. — Longitudinal  section  of  enamel  and  dentine,  after  Bodecker. 
Magnified  1,200  times.  E.R.  Enamel  rod;  E.F.  Enamel  fibre;  D.  Dentine;  D.F. 
Dentine  fibrils;  p.  Soft  protoplasmic  formations  at  the  boundary  between  both 
tissues. 

enamel  rods,  and  such  thorns  are  visible  in  all  interstices 
between  the  enamel  rods. 

The  enamel  fibres  are  continuous  on  the  outer  surface  with 
the  covering  layer  of  flat  epithelium,  and  on  the  inner  surface 
with  the  dentinal  fibres.  The  connection  with  the  latter  is 
either  direct  or  indirect  through  a  network  of  living  matter,  or 
through  intervening  protoplasmic  bodies  in  the  interzonal  layer 
(Fig.  19). 

And  also  Abbott  (op.  cit.  p.  95)  has  further  given  a  drawing 


THE   ENAMEL  29 

showing  the  enamel-rods,  the  light  reticulum  within  them,  the 
intervening  fibres,  and  the  lateral  off-shoots  of  the  fibres. 

The  researches  of  Tomes,  Leon  Williams,  and  others,  have, 
however,  demonstrated  the  fallacy  of  such  statements,  and  it 
must  surely  be  an  unpardonable  hyperbole  to  affirm  the  exist- 
ence of  a  chain  of  living  material  passing  from  the  periphery 
of  a  tooth  to  its  sentient  pulp.  The  experiments  of  Tomes  and 
Black  have  conclusively  and  for  ever  proved  the  inorganic 
nature  of  enamel. 


FIG.  21. — Vertical  section  of  normal  enamel  treated  by  Golgi's  rapid  process. 

Magnified  45  times. 

Nearly  every  section  of  normal  as  well  as  pathological  enamel, 
whether  ground  and  mounted  in  balsam  or  glycerine,  whether 
stained  or  unstained,  whether  decalcified  slightly  with  weak 
acid,  like  one  per  cent,  citric  acid,  or  prepared  under  conditions 
resembling  Nature  as  closely  as  possible,  reveals  a  certain 
degree  of  pigmentation.  If,  however,  treated  with  Golgi's 
rapid  silver  chromate  method,  this  coloration  in  normal  ground 
sections  is  intensified. 

The  enamel  of  ovarian  teeth,  deciduous  teeth,  and  nodules 
found  on  the  necks  or  roots  of  teeth,  exhibits  also  the 
pigmentation. 


THE   DENTAL   TISSUES 


FIG.  22. — Longitudinal  section  of  enamel  from  outer  surface  of  Human  in- 
cisor. Magnified  3,000  times.  The  structure  of  the  calcified  enamel-globules 
of  which  the  rods  are  composed  is  very  finely  shown  in  this  illustration.  This 
section  represents  normal  human  enamel  of  the  finest  type.  Photomicrograph 
by  Leon  Williams. 


THE   ENAMEL  31 

Of  all  investigators  in  the  difficult  subject  of  enamel  his- 
tology, the  name  of  Leon  Williams  will  ever  stand  out  pre- 
eminently. His  magnificent  work  on  the  minute  anatomy 
as  well  as  the  pathology  of  this  tissue  is  well  known,  and  he 
has  contributed  probably  by  far  the  greatest  amount  of  knowl- 
edge on  the  matter. 


FIG.  23. — Longitudinal  section  of  enamel  from  Human  tooth.  Magnified 
1,000  times.  Shows  enamel-rods  passing  through  Retzius  bands  without  break 
cif  continuity.  The  rods  are  separated  by  rather  more  than  the  normal  amount 
of  cement-substance,  and  show  imperfect  formation  in  lower  right-hand  corner. 
Photomicrograph  by  Leon  Williams. 

According  to  this  author1  enamel  rods  are  constructed  by 
the  successive  deposition  of  certain  " bodies"  formed  in  the 
enamel  cells,  a  deposition  which  goes  on  with  the  utmost  order 
and  regularity.  The  rods  possess  a  more  or  less  definite 

1  "On  the  Formation  and  Structure  of  Dental  Enamel."  The  Dental  Cosmos, 
1896. 


32  THE   DENTAL   TISSUES 

organisation.  These  "bodies"  are  beads  of  granular  material, 
which,  under  high  magnification,  are  joined  together  by  calci- 
fied plasmic  strings  and  processes  (Figs.  17  and  22).  They 
lie  exactly  opposite  each  other,  and  the  granular  strings  are 
larger  and  more  clearly  defined  on  the  extreme  margins  of  the 
enamel  rods.  Thus  Leon  Williams  has  demonstrated  indubi- 
tably that  the  "bodies"  are  connected  vertically  by  plasmic 
strings  of  granular  origin  which  traverse  the  entire  length  of 
the  rods;  that  they  are  also  united  to  the  bodies  of  con- 
tiguous rods  by  radiating  processes,  or  even  touch  one  another  at 
the  points  of  the  greatest  diameter  of  the  rods;  that  there  may 
be  as  many  as  fifteen  or  twenty  calcified  plasmic  strings  in 
each  enamel  rod;  and  that  their  ultimate  structure  is  most 
suitably  revealed  by  the  action  of  weak  acids,  such  as  citric 
in  lemon  juice,  which  first  removes  the  connecting  threads. 

The  Cementing  substance  or  matrix  varies  considerably  in 
amount.  In  the  majority  of  cases,  in  the  teeth  of  man,  the 
rods  are  more  or  less  in  actual  contact  throughout  their 
entire  course,  being  united  by  the  varicosities  or  bodies:  but 
in  some  sections  they  lie  quite  apart,  separated  sometimes  by 
matrix  which  may  equal  one-fourth  or  one-fifth  the  diameter  of 
a  column  (viz.,  i/x),  (Fig.  16).  This  translucent  intercol- 
umnar,  calcified  substance  has  in  it  delicate  connecting  lateral 
processes  and  fine,  tiny  granules,  and  does  not  contain  either 
the  organic  fibres,  which  Bodecker1  and  Abbott2  affirm  pass 
between  the  rods  and  give  off  "thorn-like"  processes,  or  the 
channels  which  have  been  described  by  von  Ebner3  (Fig.  19). 

Otto  Walkhoff,4  ex  cathedra,  refuses  to  grant  that  this  cement 
substance  exists.  He  examined  the  enamel  rods  of  certain 
Primates,  Carnivora  and  Ungulata,  in  which  the  structural 
elements  of  the  tissue  are  regular.  He  affirmed  that  vertical 
sections  of  enamel  never  give,  for  great  distances,  the  con- 

1  "The  Anatomy  and  Pathology  of  the  Teeth,"  1894. 

2  "Minute  Anatomy  of  the  Human  Tooth"  in  Trans.  Dent.  Soc.,  New  York, 
1882. 

2  "Histologie  der  Zahne"  in  "Handbuch  der  Zahnheilkunde,"  1891. 

4  "  Contributions  relating  to  the  more  minute  structure  of  the  Enamel,  and  to 
the  Development  of  Dentine."  Deutsche  Monatsschrift  fur  Zahnheilkunde, 
Jan.,  1898. 


THE    ENAMEL 


33 


tours  of  the  rods  in  one  plane,  and  that  observations  on 
such  sections  are  untrustworthy.  When  magnified  3,500 
times,  a  measurable,  thick,  doubly  coloured  stripe  was  seen: 
viewed  horizontally,  the  rods,  at  a  magnification  of  2,400, 
exhibited  no  cement  substance.  He  wrote:  "A  series  of 
photomicrographs  with  the  apochromatic  1.9  mm.  oil  immer- 
sion, objective  N.A.  1.40,  showed  that  enamel  rods  consist 
of  two  parts  optically  distinctly  divided  from  each  other. 
The  central  part,  or  real  body  of  the  rod,  is  grainless,  or,  at  the 
most,  slightly  spotted,  but  darker  coloured  than  ;me  pe- 
ripheral layer,  which  appears  whitish.  A  delicate,  somewhat 
darker  line  forms  the  border  between  the  two  layers ;  the  outer 
border  lining  the  whole  column,  which  appears  somewhat  blacker, 
is  sharply  sectioned,  even  with  high  magnifications.  Such 
pictures  are  produced  only  when  focussing  has  been  most 
exact,  and  where  possible  has  been  directed  to  the  surface  of 
the  rod.  In  its  surroundings  there  are  immediately  seen,  if 
there  is  the  slightest  obliqueness  in  the  section,  diffraction 
seams,  especially  if  oblique  illumination  has  been  used.  With 
inexact iocussing  the  picture  totally  changes.  Between  the  rods 
there  is  then  shown  a  line  which  appears  dark,  which  by  increas- 
ing the  inexactness  grows  in  width.  What  previously  was  light 
now  becomes  dark,  and  such  a  picture  gives  only  too  well  the 
delusion  of  cement  substance  between  the  enamel  rods." 

A  recurrence  to  the  belief  in  the  existence  of  an  organic 
matrix  in  the  structure  of  enamel  has  been  furnished  in  the 
pages  of  the  Deutsche  Monatsschrift  fur  Zahnheilkunde,  August, 
1902,  by  Viggo  Andresen  of  Vejle,  Denmark.  His  paper 
("Beitrag  zur  Histologie  des  Schmelzes")  is,  however,  in- 
conclusive, and  his  illustrations  unconvincing. 

It  is  interesting  to  note  the  various  opinions  and  theories  in 
connection  with  the  histology  of  enamel  and  its  rods. 
Thus: 

Abbott  says  that  "normal  enamel  is  non-striated." 

Sudduth1  denies  that  the  rods  have  any  internal  structure. 

von  Ebner  believes  in  the  existence  of  the  striae  but  considers 
they  are  an  artificial  appearance,  due  to  the  action  of  acids. 

1  "Dental  Embryology  and  Histology"  in  "American  System  of  Dentistry," 
1887. 


34  THE    DENTAL   TISSUES 

The  propositions  advanced  as  to  the  origin  of  the  shadings  or 
transverse  markings  are: 

(i)  An  intermittent  calcification  of  the  rods  would  produce 

the  dark  and  light  bands.     (Hertz.) 
(ii)  They  are  due  to  the  existence  of  beads  or  varicosities  in 

the  rods.     (Kolliker,  Waldeyer,  Haycraft,  Ewald,  and 

Leon  Williams.), 
(iii)  Or  to  inequalities  on  the  surfaces  of  the  rods.     (Sud- 

duth  and  Febiger.) 

(ii)  The  Courses  or  Curvatures  of  the  Rods 

Individually  each  rod  runs  a  more  or  less  spiral  course 
and  often  decussates  with  its  neighbours,  so  that  it  is 
exceedingly  difficult,  if  not  impossible,  to  trace  its  entire 
course. 

Collectively,  the  courses  are  neither  perfectly  straight  nor 
perfectly  parallel.  At  the  cervical  region  they  run  horizon- 
tally outwards  from  the  dentine;  at  the  cutting  edge  or  the 
masticating  surface  they  are  chiefly  set  vertically  with  it. 
They  thus  radiate  outwards  all  round.  According  to  Tomes, 
"Dental  Anatomy,"  1914,  p.  40,  "On  the  whole  the  rods  are 
parallel  and  run  from  the  surface  of  the  dentine  continuously 
to  that  of  the  enamel.  Their  paths  are  not,  however,  either 
perfectly  straight  or  perfectly  parallel;  for  alternate  layers 
appear  to  be  inclined  in  opposite  directions,  while  they  are  also 
wavy,  forming  several  curves  in  their  length.  The  curvature 
of  the  rods  is  most  marked  on  the  masticating  surface:  while 
the  layers,  alternating  in  the  direction  of  their  inclination, 
as  just  described,  are  in  places  transverse  to  the  long  axis  of 
the  crown,  and  correspond  to  the  fine  imbrication  lines  on  the 
surface  of  the  enamel,  which  appear  to  be  caused  by  their 
outcrop.  The  curvatures  take  place  in  more  than  one  plane; 
in  other  words,  the  course  of  the  individual  rod  is  more  or 
less  a  spiral." 

A  general  idea  of  the  courses  of  the  rods  may  be  obtained 
by  macroscopic  examination  of  a  section.  - 


THE    ENAMEL 


(iii)  The  Brown  Striae  of  Retzius 

Nearly  every  longitudinal  section  of  enamel  exhibits  in  a 
more  or  less  degree  these  stripes.     They  appear  as  shadings 


PIG.  24. — Vertical  section  of  Human  enamel.  Unstained,  and  non-decal- 
cified. Magnified  250  times.  The  lines  which  run  across  the  rods  are  cracks 
in  the  tissue  produced  by  grinding  the  section. 

or  brown  markings,  arranged  in  the  form  of  arcuate  stripes; 
and  they  maintain  a  certain  amount  of  parallelism   to   the 


30  THE   DENTAL   TISSUES 

boundary-line  of  enamel  and  dentine,  which  may  be  called  the 
amelo-dentinal  junction  (Fig.  25).  Crossing  the  columns  in 
various  planes  and  in  various  directions,  they  are  more  pro- 
nounced on  the  cortical  portions  of  the  tissue,  but  extend  right 
up  to  the  junction.  Between  thirty-six  and  forty  have  been 
counted  as  crossing  a  segment  of  enamel,  but  the  number  varies 
very  greatly.  The  bands  are  interrupted  partially  or  com- 


FIG.    25. — The  Brown  Striae  of  Retzius  in  enamel.     Prepared  by  grinding  thin. 
Unstained.     Magnified  40  times.     E.  Enamel;  D.  Dentine.     , 

pletely.  Sudduth  calls  them  "the  broken  striae,"  etc.  Many 
are  broad  and  many  are  narrow,  the  thickest  and  most  marked 
of  the  former  measuring  sometimes,  roughly,  one-fifteenth  part 
of  the  whole  thickness  of  the  enamel.  These  stratifications 
are  only  visible  in  vertical  sections.  Horizontally,  the  stripes 
are  cut  obliquely  or  transversely,  and  thus  are  seen  as  concen- 
tric bands,  darker  and  more  distinct  at  the  edge  than  near  the 
dentine;  and  therefore  they  give  the  enamel  a  more  or  less 
lamellated  appearance. 

The  striae  of  Retzius  are  due  to  pigmentary  deposition  in  the 
rods.     The  theories  propounded  by  von  Ebner  and  Kolliker 


THE   ENAMEL  37 

have  been  dismissed  by  Leon  Williams  as  incorrect.  The 
former  observer  supposes  that  the  bands  are  due  to  "imprisoned 
air  or  gas  which  has  entered  the  ground-off  ends  of  the  rods 
through  minute  channels."  And  to  this  Leon  Williams  replies 
(op.  cit.  page  475)  that  the  idea  is  a  mistaken  one,  "first, 
because  the  supposed  canals  have  no  existence;  secondly,  be- 
cause the  ground-off  ends  of  enamel  rods  do  not  appear  except 
when  the  section  of  enamel  is  ground  at  a  certain  angle." 

According  to  Walkhoff  (loc.  cit.}  the  striae  of  Retzius  are 
nothing  else  than  the  ordinary  transverse  striping  of  the  enamel 
rods  on  a  large  scale.  He  declares  that  both  striae  are  the 
expression  of  the  deposition  by  the  lime  salts  of  the  enamel- 
tissue  strata-wise,  a  longer  lasting  interruption  of  the  calcifying 
process  producing  the  Retzian  stripes,  and  one  short,  often- 
repeated,  the  transverse  striae  of  the  prisms. 

Thus  the  brown  striae  of  Retzius  have  been  attributed  in 
their  origin  to: — 

(i)  The    lamella  ted    mode    of    formation    of    the    enamel; 

(Kolliker,  Walkhoff.) 
(ii)  The  entrance  of  air  into  cavities  between  enamel  rods; 

(von  Ebner.) 

(iii)  The  varying  character  of  food  taken  by  the  mother 
during  the  period  of  gestation,  some  food  being  rich  in 
lime  salts  of  one  kind  and  some  rich  in  salts  of 
another  kind;  ("American  System  of  Dentistry,"  p. 
656,  1887.) 

(iv)  And  finally,  and  correctly,  pigmentation.  (Leon 
Williams.) 

(iv)  The  Lines  of  Schreger 

By  reflected  light,  as  well  as  by  transmitted  light,  it  is  often 
possible  to  distinguish  in  ground  perpendicular  sections  of 
the  teeth  of  man,  entire  band-shaped  layers  of  rods  alter- 
nately decussating  in  such  a  manner  as  to  produce  lines.  By 
the  former,  they  appear  white,  by  the  latter  black,  as  in  the 
photomicrograph.  These  differ  very  markedly  from  the  striae 
of  Retzius,  inasmuch  as  they  run  transversely  to  them  (Fig.  26) 


THE   DENTAL   TISSUES 


FIG.  26. — Vertical  section  of  Human  enamel  shewing  the  lines  of  Schreger. 
Section  ground  thin.  Unstained.  Magnified  45  times.  E.  Free  surface  of  the 
enamel;  s.  Schreger 's  lines;  D.  Dentine.  r 


FIG,  27. — Same  as  preceding  figure.     Magnified  250  times. 


THE    ENAMEL 


39 


and  are  long,  level,  very  broad  bands,  which  bear  some  resem- 
blance to  flat  clouds  (Fig.  28)  of  the  cumulo-stratus  type. 
All  sections  by  no  means  exhibit  them;  but  those  specimens 
which  do,  commonly  shew  them  most  clearly  and  distinctly. 
They  blend  together,  and  therefore  form  blackish  masses  in  the 
enamel.  They  may  be  distributed  anywhere  throughout  the 
thickness  of  the  tissue,  but  very  often  are  confined  to  its 
inner  aspect,  particularly  at  the  cusps  of  premolars  and  molars. 


FIG.  28. — Schreger's  lines  in  enamel,  as  cloud-like  masses  through  dense 
pigmentation.  Magnified  300  times,  s.  Schreger's  lines;  D.  Dentine  with 
enamel  spindles. 

High  powers  reveal  the  fact  that  the  rods  are  histologically 
normal,  and  it  is  only  low  magnifications  which  make  apparent 
their  occasional  lengthwise  groupings. 

(v)  Certain  Spaces  or  "Enamel  Spindles" 

Independent  of  certain  cavities  or  clefts  on  the  free  surface 
of.  enamel,  which  have  no  special  structure,  there  can  often 
be  found  in  teeth  free  from  any  apparent  structural  defects, 
near  the  amelo-dentinal  junction,  irregularly  shaped  chasms, 
which  in  ground  sections  are  remarkably  clear  and  brilliant 
(see  Fig.  31).  They  appear  to  be  in  direct  continuity  with 


THE    DENTAL   TISSUES 


FIG.  29. 


FIG.  30. 

FIGS.  29  and  30. — Vertical  sections  through  cusps  of  Human  molar.  Stained 
with  Golgi's  rapid  process.  Magnified  45  times.  E.  Enamel;  D.  Dentine; 
F.  Fissure  with  clear  structureless  margins. 


THE   ENAMEL  41 

those  few  dentinal  tubes  which  manage  to  cross  the  boundary 
line  of  the  two  hard  tissues.  In  fact  they  resemble  bulbous 
enlargements  of  the  tubes  (Fig.  32).  Situated  between  the  rods, 
in  the  cement  substance,  which,  according  to  von  Ebner,  and 
quoted  by  Romer  in  his  "  Zahnhistologische  Studie,"  1899, 
p.  39,  is  more  abundant  near  the  dentine  than  the  cortex, 
they  run  vertically  outwards,  are  narrow,  and  about  40/1  long. 
They  may  be  clubbed  or  spindle-shaped. 


FIG.  31. — Vertical  section  through  cusps  of  tooth.  Magnified  50  times. 
E.  Enamel;  D.  Dentine,  many  tubes  of  which  end  in  the  enamel  spindles. 
Photomicrograph  by  Douglas  Gabell. 

These  spaces  are  not  infrequently  observed  in  vertical  ground 
sections  of  molars  or  premolars. 

In  the  margins  of  the  apices  of  the  dentine  cusps  (Fig.  33) 
they  are  more  numerous  than  in  the  saddle-shaped  depressions 
between  them,  in  which  situation  they  are  only  to  be  met 
with  singly  or  in  sparse  numbers.  The  knobs  sit  on  the  den- 
tinal tubules  exactly  like  ears  on  the  stems  of  the  straw  of 
corn  bound  up  into  sheaves.  Those  found  in  the  highest 
parts  of  the  cusps  appear  to  stand  upright;  while  on  the  con- 


THE  DENTAL   TISSUES 


K 


FIG.  33. 

FIGS.  32  and  33. — Adapted  from  two  drawings  by  Kretz,  in  Romer's 
"  Zahnhistologische  Studie,"  1899.  Fig.  32. — Vertical  section  through  amelo- 
dentinal  junction  in  molar  of  a  child,  stained  with  gold  chloride,  and  potassium 
iodide.  Magnified  1,500  times.  D.  Dentine;  E.  Enamel;  T.  Dentinal  tube; 
K.  Enamel  spindle;  c.  Dark  red  corpuscle  in  the  interior  of  the  enamel  spindle. 
FIG.  33. — Vertical  section  through  the  amelo-dentinal  junction  of  a  cusp  of  a 
left  maxillary  first  molar  of  a  boy,  aged  13  years.  Stained  as  in  last  Figure. 
Magnified  250  times.  E.  Enamel;  D.  Dentine;  K.  Enamel  spindles. 


THE    ENAMEL  43 

trary  those  at  the  slopes  incline  more  or  less  to  the  horizontal 
plane.  Thus,  in  a  longitudinal  ground  section  through  the 
middle  of  the  cusp  they  are  cut  perpendicularly,  whereas  in  a 
tangential  ground  section  going  through  the  lower  portion 
they  are  found  for  the  most  part  cut  transversely. 

In  sections  ground  in  the  ordinary  way,  and  subsequently 
treated  in  the  usual  manner,  these  enamel-knobs  stand  out 
black  or  dark  grey  on  a  light  background.  There  is  no  internal 
structure  visible,  the  space  being  filled  with  detritus,  etc., 
from  the  act  of  grinding. 

Whether  protoplasm  ever  filled  them  is  a  difficult  matter  to 
decide.  It  is  probable  that  in  the  fresh  condition  it  did. 

Various  accounts  are  given  by  different  authors  as  to  their 
histological  characteristics,  amongst  whom  Tomes,  von  Ebner,1 
Hollander,2  Wedl,3  Bodecker,4  and  Oscar  Romer5  may  be  cited. 

Charles  Tomes  (op.  cit.  p.  49)  makes  no  mention  of  their 
contents,  and  concludes  that  "perhaps  they  are  to  be  regarded 
as  pathological." 

That  hollow  spaces  constitute  these  enamel-spindles  von 
Ebner  and  Wedl  are  agreed:  but  the  former  holds  that  they 
contain  air,  and  the  latter  that  they  are  filled  with  amorphous 
dark  calcareous  masses,  von  Ebner  thinks  they  are  actually 
produced  by  the  shrivelling  up  of  the  cement  substance,  which 
is  more  easily  possible  at  the  amelo-dentinal  line  than  at  the 
free  surface  of  the  tissue.  Hollander  describes  their  presence 
in  the  juxta-dentinal  zone  of  enamel,  but  regards  them  as  non- 
pathological.  Bodecker  says  "They  invariably  contain  proto- 
plasmic bodies  of  distinctly  reticular  structure  and  sometimes 
one  or  more  compact  clusters,  which  may  be  spoken  of  as  nuclei. 
The  spindle-shaped  corpuscles  stand  at  their  central  terminations 
in  direct  connection  with  the  ends  of  the  dentinal  fibres,  as 
these  originated  from  repeated  branchings.  At  many  places, 
especially  those  corresponding  to  the  crown  apices,  the  spindle- 
shaped  enlargements  of  the  dentinal  fibres  are  very  numerous, 

1  Scheff's  "Handbuch  der  Zahnheilkunde,"  Vienna,  1891. 

2  "Die  Anatomic  der  Zahne  des  Menschen  und  der  Wirbelthiere,"  Berlin,  1877. 

3  "Pathologic  der  Zahne,"  Leipzig,  1870. 

4  Heitzmann's  " Mikroscopische  Morphologic,"  Vienna,  1883. 

8  N erven  in  Zahnbein,  "Zahnhistologische  Studie,"  Freiburg,  1899. 


44 


THE    DENTAL   TISSUES 


and  nearly  regular  in  size  and  direction.  .  .  .  In  the  teeth 
of  younger  persons  the  spindle-shaped  swellings  are  relatively 
larger  and  more  regular  than  in  those  of  older  people."  This 
is  called  the  "Bio-plasson  theory." 

Romer  coincides  on  the  whole  with  Bodecker's  view,  with 
the  reservation  that  he  would  apply  the  term  "dentinal 
tubules,"  instead  of  "  dentinal  fibres,"  to  those  formations 
which  widen  out  into  clubs  or  spindles  in  the  enamel.  He 
declares  that  the  spaces  contain  an  organic  matter  capable 


E  s 


D   N 


FIG.  34. — Vertical  section  through  the  coronal  part  of  a  tooth.  Prepared  by 
Weil's  process.  Magnified  250  times.  E.  Enamel;  D.  Dentine;  E.S.  Enamel 
spindle  critically  focussed  to  shew  Romer's  corpuscles. 

of  becoming  stained  with  chloride  of  gold,  and  appear  of  a 
reddish  tint,  varying  from  a  rose-colour  to  a  dark-red  hue 
(marked  C  in  Fig.  32).  He  admits  that  in  most  cases  they 
are  merely  filled  with  air,  through  the  shrinking  of  some  of 
the  organic  material;  but  affirms  that  when  teeth  are  treated 
by  the  Koch-Weil  method  there  is  no  shrinkage,  and  that  a 
non-reticulated  organic  substance  is  really  present  inside  the 
knob.  He  describes  and  figures  (Fig.  xxxiii.,  Tafel  vii.)  in  one 
space  "several  spherical  corpuscles  hanging  together  by  a  fine, 


THE    ENAMEL  45 

scarcely  measurable  fibre,  also  stained  dark-red  and  running 
out  into  a  fine  point"  (see  Fig.  32,  also  Fig.  34).  In  conclusion, 
he  writes: — "I  should  not,  however,  call  these  round  or  oval 
corpuscles  cell-nuclei,  as  Bodecker  does;  especially  I  cannot, 
like  him,  in  defending  his  'Bio-plasson'  theory,  testify  to  a 
connection  between  these  knobs  and  'the  living  enamel 
material ; '  but  I  think  we  should  much  rather  venture  to  see  in 
these  fine  corpuscles,  so  often  arranged  in  rosary-like  order, 
sensitive  nerve-end  apparatus  of  the  nerve  filaments  which  run 
in  the  dentinal  tubules."  For  the  arguments  which  Romer 
advances  in  favour  of  this  extraordinary  hypothesis,  see  his 
paper. 

The  tubes  of  the  dentine  themselves  often  traverse  the 
boundary  line  and  penetrate  the  enamel  sometimes  to  a  depth 
of  30ju.  They  run  in  the  cement  substance,  not  in  the  interior 
of  the  rods. 

Before  altogether  dismissing  these  theories,  one  or  two  more 
instances  may  be  given  of  other  opinions  on  this  most  interest- 
ing subject. 

F.  T.  Paul  (The  Dental  Record,  p.  495,  1896)  explains  their 
occurrence  in  this  manner:- — "In  early  mammalian  tooth- 
germs,  the  ameloblasts  and  odontoblasts  are  seen  to  be  sepa- 
rated by  a  thin  band  of  transparent  dentine  matrix,  due  to 
certain  changes  in  the  surface  of  the  pulp.  This  band  has 
two  sets  of  processes  of  formed  matrix.  One,  as  Howard 
Mummery  first  showed,  passes  between  the  odontoblasts  to 
communicate  with  the  connective  tissue  matrix  of  the  pulp,  and 
the  other  extends  outwards  between  the  ameloblasts,  which, 
in  some  instances,  are  therefore  kept  apart,  and  thus  form 
elongated  spaces  filled  with  the  imperfectly  calcified  matrix 
of  dentine.  'That  processes  of  dentine  matrix  thrust  up 
between  the  enamel  rods  should  never  calcify,  is  certainly 
nothing  surprising  when  one  remembers  that  the  first  layer 
of  dentine  usually  only  calcifies  imperfectly,  being  character- 
istically the  site  of  the  interglobular  spaces  of  Tomes.' ' 

Waldeyer  (in  Strieker's  "Handbuch  cler  Lehre  von  den 
Geweben,"  Leipzig,  1871)  denies  that  the  spindle-shaped  spaces 
in  enamel  exist  at  all,  as  structural  elements,  either  as  develop- 


46  THE    DENTAL   TISSUES 

mental  errors  or  pathological  lesions.  He  bases  his  view  on  the 
assumption  that  the  least  defect  in  the  parallelism  of  the  sections 
would  be  likely  to  lead  to  incorrect  appearances.  Cracks  or 
fissures  in  the  enamel,  produced  by  manipulative  interference, 
would  also  yield  deceptive  results.  Hertz,  too,  another  of  the 
earlier  investigators,  interpreted  the  meaning  of  these  spaces 
in  a  similar  way. 

But  Walkhoff1  has  often  seen  them. 

One  of  the  most  difficult  problems  in  the  whole  of  dental 
histology  is  that  connected  with  the  relationship  of  enamel 
and  dentine;  for  not  only  is  it  hard  to  conceive  how  enamel, 
an  ectodermic  substance,  should  be  so  securely  fixed  on  the 
surface  of  a  mesodermic  substance,  and  by  what  means  they  are 
thus  bound  together;  but  the  transpiercing  of  the  amelo- 
dentinal  boundary  by  the  dentinal  tubes  is  infinitely  still  more 
perplexing.  Walkhoff  has  published  (op.  cit.)  an  ingenious 
hypothesis  in  attempting  to  explain  this  phenomenon.  In 
common  with  Wedl  (op.  cit.}  and  vori  Ebner,  he  assumes  that 
at  this  border-line  there  must  have  been  an  absorption  of  the 
first  deposited  dentine.  His  arguments  in  favour  of  this  are 
founded  on  the  facts  that  under  the  enamel,  Tomes'  granular 
layer  is  never  seen,  because,  though  once  existing,  it  has  in  the 
process  of  time  become  absorbed:  that  the  dentinal  canals 
run  up  to  the  edge  without  much  narrowing  of  their  diameters, 
thus  apparently  proving  that  they  have  been  diminished  in 
length:  and,  finally,  that  here,  too,  there  are  practically  no 
branchings,  these  having  disappeared  in  consequence  of  the 
resorptive  process. 

Granting  that  the  interpretations  of  these  phenomena  are 
correct,  he  proceeds  to  explain  that,  owing  to  an  especial 
vitality  on  the  part  of  certain  individual  tubes,  they  are  enabled 
to  completely  resist  the  absorption  of  the  defectively  built 
dentine  which  is  going  on  all  round,  remain  in  situ,  and,  there- 
fore, have  the  appearance  of  actually  projecting  beyond  the 
amelo-dentinal  junction.  Walkhoff  adds  that  the  canals  appear 
as^if  sharply  cut  off,  a  proof  that  their  terminations  are  absorbed. 

1  Deutsche  Monatsschrift  fur  Zahnheilkunde,  January,  1898;  also  "Die  Normale 
Histologie  Menschlicher  Zahne,"  Leipzig,  1901. 


THE    ENAMEL 


47 


The  direction  of  their  courses  is  not  always  parallel  with  the 
enamel  columns,  because  they  frequently  break  through  the 
rods  transversely.  There  occur  formations  (the  enamel-knobs) 
at  the  apices  of  the  dentine  cusps  in  the  teeth  of  Primates  and 
Carnivora,  which  may  reach  far  into  the  enamel,  and  do  not 
consist  of  simple  dentine  tubes,  but  may  have  round  them  a 
large  amount  of  uncalcified  basis  substance  or  matrix. 


FIG.  35. — Vertical  section  through  coronal  region  of  a  tooth,  shewing  the 
amelo-dentinal  junction.  Prepared  by  grinding.  Unstained.  Magnified  250 
times.  E.  Enamel;  D.  Dentine;  s.  Granular  enamel  rods  of  irregular  formation. 

Walkhoff  summarises  his  investigations  by  asserting  that 
the  club-like  processes  represent  simple  dentinal  tubes,  which, 
through  unusual  vitality,  have  opposed  sufficient  resistance  to 
the  absorption  of  the  dentine,  which  takes  place  during  the 
formation  of  the  enamel;  and  that  there  were  certain  masses 
of  basal  substance  already  formed  round  each  tube  which  the 
resorption  was  unable  to  destroy. 

The  amelo-dentinal  line,  junction,  or  boundary,  is  made  up  of 
a  fairly  straight  or  slightly  undulating  line  with  pale  homo- 
geneous tissue  on  either  side.  The  tubules  do  not  end  on  the 
line,  but  near  it,  while  the  enamel  rods  themselves  are  struc- 


48  THE    DENTAL   TISSUES 

tureless  or  faintly  granular.  This  condition  obtains  in  hori- 
zontal sections  of  premolar  and  molar  teeth  taken  at  the 
cervical  margin,  and  at  the  narrow  part  of  that  margin.  In 
its  broadest  part  the  boundary  is  represented  by  a  linear 
series  of  tiny  enamel  convexities  looking  towards  the  dentine. 
Here  the  tubules  are  strong  and  thick  and  come  quite  up  to 
the  edge  of  the  convexities,  and  the  structure  of  the  enamel 
convex  surface  is  pale,  bright,  and  glistening  when  viewed  by 
transmitted  light  (Fig.  35).  The  enamel  in  the  immediate 
neighbourhood  is  translucent  and  structureless.1 

The  same  appearance  is  found  in  vertical  sections,  but  the 
enamel  crescents  are  more  constant.  They  closely  resemble 
that  edge  of  the  layer  of  formed  but  uncalcified  dentine — the 
dentogenetic  zone — in  developing  teeth  which  is  in  juxta- 
position to  the  calcified  dentine. 

As  has  been  already  stated,  tubules  from  the  dentine  with 
or  without  their  bulbous  enlargements  occasionally  cross 
this  border. 

1  It  is  of  great  interest  to  note  that  when  sections  of  sound  teeth  have  been  sub- 
jected to  impregnation  with  coloured  collodion,  as  first  advocated  by  Charters 
White,  isolated  patches  of  the  enamel  of  this  region  may  become  stained.  (See 
Fig.  35.)  This  often  occurs,  and  may  show  that  the  chemical  properties  of  the 
enamel  are  different  here.  The  fact  may  probably  throw  some  light  on  the 
actual  method  of  production  of  secondary  enamel  decay;  and  may  be  regarded 
as  an  evidence  of  degeneracy  of  human  enamel. 


CHAPTER  IV 
ORTHO -DENTINE 

MICROSCOPICAL  ELEMENTS. — (i)  Matrix;  (ii)  Tubes;  (iii)  Sheaths  of 
Neumann;  (iv)  Interglobular  spaces;  (v)  Granular  layer;  (vi) 
Schreger's  Lines;  (vii)  Contour  lines  of  Owen;  (viii)  Laminae.  Second- 
ary dentine. 

GENERAL   CHARACTERISTICS 

Definition.— That  hard  tissue1  of  the  tooth,  which,  while 
comprising  its  greatest  bulk,  forms  the  natural  boundary  of 
its  pulp. 

Varieties. — There  are  four  varieties: — Ortho-dentine—hard 
or  unvascular  plici-dentine,  vaso-dentine,  and  osteo-dentine. 
This  is  Tomes'  classification.  Dr.  Med.  C.  Rose,2  of  Leipzig, 
basing  his  opinion  on  the  definition  of  dentine  as  "a  hard  tissue 
with  a  smooth  surface,  which  is  developed  under  an  epithelial 
sheath  (enamel  organ),  and  grows  on  one  side  only,"  groups 
the  different  kinds  under  the  headings  of  (i)  "Normal  tubular 
dentine,"  (ii)  "Vitro-dentine"  which  contains  no  protoplasmic 
processes,  (iii)  "the  Vaso-dentine  of  Tomes,"  and  (iv)  "Tra- 
becular  dentine."  The  latter — a  new  term — is  defined  as  "a 
hard  tissue,  rich  in  short  dentinal  canals,  and  capable  of  in- 
crease in  all  directions;  but  not  growing  immediately  beneath, 
and  in  dependence  upon  an  epithelial  sheath."  Here  will  be 
considered  the  first-named  variety,  viz.,  hard  dentine,  or,  more 
correctly,  ortho-dentine.3 

1  According  to  Gallippe  (Comp.  Rend,  des  Seances  el  Memoircs  de  la  Societe  de 
Biologic,  1884)  the  chemical  constituents  of  dentine  are  as  follow:  Phosphoric 
acid,  23.70  per  cent.;   Calcium,  45.11  per  cent.;   Magnesium,  1.67  per  cent.; 
Magnesium  Carbonate,  i.i3percent.;  Calcium  Carbonate,  0.35  per  cent.;  Silicates, 
0.41  per  cent.;  Alkaline  chlorides  and  phosphates,  0.54  per  cent.;  water  and 
organic  matter  (probably  collagen),  25.29  per  cent.;  and  an  unknown  salt,  1.8 
per  cent. 

2  "On  the  various  alterations  of  the  Hard  Tissues  in  the  lower  vertebrate 
animals."     From  the  Anatomischer  Anzieger,  1898.     (Bd.  xiv.,  Nos.  i,  2,  and  3.) 

3  In  the  following  pages  the  use  of  the  word  "dentine"  is  applied  to  the 
commoner  variety,  viz.,  ortho-dentine, — unless  otherwise  indicated.  : 

49 


50  THE    DENTAL    TISSUES 

Origin. — The  matrix  or  intertubular  ground  substance  is 
formed  by  calcification  proceeding  from  certain  cells  of  the 
pulp;  the  walls  and  contents  of  the  tubules  are  manufactured 
probably  by  the  columnar  cells  on  the  surface  of  the  pulp, 
these  as  well  as  the  other  cells  being  derived  from  the  stomo- 
daeal  mesoderm.1 

Distribution.—  Hard  unvascular  dentine  is  found  in  the 
teeth  of  man,  and  most  mammals;  also  in  some  reptiles  and 
fishes.  In  the  adult  human  dentition  it  measures  about  2  mm. 
in  the  radicular,  and  4  mm.  to  5  mm.  in  the  coronal  regions,  over 
the  cornua  of  the  pulp. 

Macroscopical  Appearances.- — Yellowish- white  in  colour,  dull, 
and  slightly  lustrous  on  cleavage. 

HISTOLOGY 

In  considering  the  minute  anatomy  of  dentine,  it  will  be 
convenient  to  describe  its  (i)  Matrix,  (ii)  tubes,  (.iii)  sheaths 
of  Neumann,  (iv)  interglobular  spaces,  (v)  granular  layer, 
(vi)  lines  of  Schreger,  (vii)  contour  lines  of  Owen,  and  (viii) 
lamellae  or  laminae. 

(i)  The  Matrix 

The  matrix,  or  inter-tubular  substance,  called  also  the 
basis-substance  by  some  authors,  appears  to  be  perfectly 
homogeneous,  translucent  and  hyaline.  The  researches  of 
von  Ebner2  (who  first  successfully  demonstrated  the  existence 
of  a  connective  tissue  stroma  in  bone)  and  Howard  Mummery 
(Philosoph.  Trans.  Roy.  Soc.,  1892),  have,  however,  proved  that 
a  delicate  network  of  fine  connective  tissue  fibres  pervades  it. 
The  latter  says  (p.  537)  "We  can  no  longer  look  upon  the 

1  Throughout  these  pages  the  conventional  use  of  the  word  "odontoblast" 
(meaning  each  of  the  large  columnar  cells  on  the  surface  of  the  pulp)  will  be 
retained.  The  author's  view  as  to  the  term  being  a  misnomer  when  applied  to 
these  cells  is  well-known;  the  reader  is,  however,  referred  to  a  Note  in  the 
Appendix  for  the  arguments.  It  may  be  possible,  a  few  years  hence,  to  properly 
attach  the  name  to  the  other  round  central  pulp  cells,  and  not  to  the  constituents 
of  the  membrana  eboris,  which  may  be  designated  "pulp  corpuscles." 

"Histologie  der  Zahne  mit  Einschluss  der  Histogenese,"  in  Scheff's  "Hand- 
buch  der  Zahnheilkunde,"  Vienna,  1891. 


THE   DENTINE  51 

matrix  of  dentine  as  being  a  homogeneous  substance,  but  must 
regard  it  as  composed  of  a  reticulum  of  fine  fibres  of  connect- 
ive tissue,  modified  by  calcification,  and  when  that  process 
is  complete,  entirely  hidden  by  the  densely  deposited  lime 
salts." 


FIG. 


FIG.  37. 


FIG.  36.  —  Longitudinal  section  at  apex  of  radicular  portion  of  pulp  in  Human 
premolar,  shewing  odontogenic  fibres  in  continuity  with  the  dentogenetic  zone. 
Magnified  350  times.  (After  a  drawing  by  Howard  Mummery  in  the  Philosoph. 
Trans.  Royal  Society.) 

FIG.  37.  —  Transverse  section  of  pulp  of  crown  of  a  Human  premolar,  shewing 
fine  fibres  in  connection  with  the  dentine  on  one  side,  and  the  pulp  on  the  other, 
crowded  with  cell  nuclei.  Magnified  230  times.  (After  a  drawing  by  Howard 
Mummery  from  the  same  source.) 


FIG.  38. — Same  as  preceding  drawing,  and  from  the  same  source.      The  larger 
nuclei  belong  apparently  to  odontoblasts.      Magnified  230  times. 

"These  fibres  decussate  freely  with  one  another,  and  I 
believe  them  to  be  analogous  to  the  decussating  fibres  of  bone. 
They  are  rendered  visible,  in  some  instances,  by  the  slow 
decalcifying  action  of  caries,  as  they  appear  to  resist  the 


THE   DENTAL   TISSUES 


action  of  acids  more  than  do  the  lime  salts."     He  suggests  for 
these  the  term  "odontogenic  fibres."     They  are,   therefore, 


FIG.  39. — Odontogenic  fibres.     (Photomicrograph  by  Howard  Mummery.) 


FIG.  40. — Same  as  preceding  figure.     (Photomicrograph  by  Howard  Mummery.) 

most  likely,    morphologically   and   chemically,  identical  with 
those  found  in  the  matrix  of  the  bone,  and  have  their  origin  in 


THE    DENTINE  53 

connection  with  or  are  closely  attached  to  certain  connective 
tissue  fibres  of  the  pulp.     They  are  uncalcified. 

(ii)  The  Tubes  or  Tubules 

The  microscopical  examination  of  a  section  of  dentine, 
whether  lengthwise,  crosswise,  or  oblique,  whether  decalcified 
or  not,  discloses  the  fact  that,  interpenetrating  it  everywhere, 
are  very  numerous,  fine,  ramulous,  fastigiated  fibril-transmitting 
channels.  Ground  sections  exhibit  the  tubes  better  than  those 


OF 


FIG.  41. — Odontogenic  fibres  in  a  vertical  section  of  carious  dentine,  the  de- 
calcification  of  which  has  rendered  them  very  apparent.  The  crown  of  a  molar 
tooth  of  man.  Decalcified  by  the  author's  process.  Stained  with  Ehrlich's 
acid  haematoxylene.  Magnified  420  times.  D.  Dentine;  p.  Pulp;  O.F.  Odonto- 
genic fibres. 

chemically  softened,  because  they  retain  debris  and  air,  and 
are  thus  more  strikingly  differentiated  from  the  matrix. 

When  viewed  vertically,  it  is  at  once  apparent  that  the 
tubes  run  centrifugally  and  radially  from  the  pulp-cavity. 
They  maintain  a  certain  amount  of  coincidence  with  the 
direction  of  the  peripheral  cells  of  the  pulp  (the  so-called 
odontoblasts)- — that  is,  they  leave  the  soft  tissue  in  lines 
nearly  always  continuous  with  the  long  axes  of  the  odontoblasts. 


54 


THE    DENTAL   TISSUES 


FIG.  42. — Vertical  section  of  dentine,  coronal  portion,  showing  the  arrange- 
ment of  the  primary  curvatures  of  the  tubules.  Unstained.  Magnified  40 
times.  E.  Enamel;  D.  Dentine;  F.  Interglobular  spaces. 


THE   DENTINE 


55 


FIG.  43.— Vertical  section  of  dentine,  radicular  portion,  showing  the  branch- 
ing and  terminations  of  the  tubules.  Prepared  by  grinding,  after  staining  by 
impregnation  with  '-coloured  collodion.  Magnified  240  times.  D.  Dentine- 
c.  Cementum. 


THE    DENTAL   TISSUES 


FIG  44. — Transverse  section  of  dentine,  radicular  portion,  showing  the  radia- 
tion of  the  tubes  from  the  pulp  cavity.  Prepared  by  grinding.  Unstained. 
Magnified  40  times.  D.  Dentine;  c.  Cementum. 


THE   DENTINE  57 

They  are  arranged  side  by  side  in  an  approximately  parallel 
manner  to  each  other. 

In  width  they  vary  from  I.J/JL  to  2.2/1,  or  5/1  (Kolliker); 
2.5/z  (Owen);1  or  0.0055  mm- — an  average  measurement- — at 
their  pulpar  or  large  extremity  (Schafer  in  "Quain's  Anatomy," 
Vol.  II.,  Part  I.,  1912).  The  distance  between  their  mouths 
may  be  considered  to  be  twice  or  thrice  their  diameter  in  the 
same  situation,  where,  too,  it — the  distance —  is  fairly  regularly 


FIG.  45. — Longitudinal  section  of  dentine.      Prepared  by  grinding.      Unstained. 
Magnified  420  times. 

maintained.  No  hard-and-fast  statement  can,  however,  be 
made  on  this  point,  as  the  amount  of  intervening  matrix  is 
greater  or  less  in  different  parts  of  the  tooth  and  of  the  teeth 
in  the  same  mouth.  The  diameter  of  the  tubes  diminishes  as 
it  proceeds  outwards,  till  at  the  cervical  region  of  the  tooth  it 
becomes  immeasurable.  Their  greatest  lengths  may  equal  from 
5  mm.  to  6  mm. 

The  inner  extremity  of  a  canal  is  a  wide  open  orifice  looking 
on  to  the  surface  of  the  pulp;  the  other  near  the  enamel   or 

1  "Odontography,"  p.  459,  1840. 


THE    DENTAL   TISSUES 


FIG.   46. — Dentine.      Nearly  transverse  section.      Prepared  by  grinding. 
Stained  bv  Weil's  process.       Magnified  160  times. 


FIG.  47. —  Dentine.     Oblique  section,  showing  the  branches  of  the  tubes.     Pre- 
pared as  in  last  figure.     Magnified  420  times. 


THE    DENTINE 


59 


cementum  is  a  cul-de-sac  of  large  dimensions  in  the  former 
locality,  and  generally  one  or  more  minute  spherical  knobs 
in  the  latter.  Those  in  the  coronal  part  of  the  tooth  run 
vertically  from  the  pulp  cavity,  at  the  cervical  margin  obliquely, 
and  in  the  radicular  region  horizontally  or  with  an  inclination 
towards  the  apex.  This  difference  in  direction  is  gradually 
brought  about,  and  varies  considerably  in  different  specimens 
(Fig.  42). 


FIG.  48. — Dentine,  radicular  portion,  showing  secondary  curvatures  of  the  tubes. 
Magnified  160  times.      (Photomicrograph  by  Douglas  Gabell.) 


Each  tube  describes  in  its  somewhat  divergent  course  certain 
curves  or  flexures.  These  are  called  the  "primary"  and 
"secondary"  curvatures  of  the  dentinal  tubules.  The  former 
are  more  marked  in  the  crown  than  the  root,  the  latter  the 
root  than  the  crown;  the  former  are  large,  gentle  undulations, 
the  latter  small  spiral  twists;  the  former  are  on  the  same  plane 
or  nearly  so,  the  latter  not  on  the  same  plane;  the  former  two 
or  three  in  number,  the  latter  very  numerous,  as  many  as  two 
hundred  in  a  line — H2  of  an  inch — according  to  Retzius. 


6o 


THE    DENTAL    TISSUES 


Welcker  has  likened  a  tubule  to  "the  thread  of  a  corkscrew 
stretched  so  that  the  turns  are  drawn  far  apart,"  its  breadth 
thereby  being  proportionately  diminished.  In  thick  longitu- 
dinal and  transverse  sections  of  the  dentine  of  the  root  this 
corkscrew-like  appearance  is  easily  noted  (Fig.  48). 

The  tubules  of  dentine  in  deciduous  teeth  are  sometimes 
constricted  at  short  intervals,  and  thus  present  a  moniliform 
appearance. 


FIG.  49. — Dentine.  Coronal  portion,  showing  tubes  and  spherical  dilatations 
of  the  termination  of  the  branches.  Prepared  by  grinding.  Unstained.  Magni- 
fied 160  times.  D.  Dentine;  E.  Enamel;  A.  Amelo-dentinal  junction. 

Further,  at  the  cervical  regions  of  the  deciduous  teeth  the 
tubes  make  a  conspicuous,  sudden,  extensive  bend  in  their 
courses,  in  addition  to  the  primary  and  secondary  curvatures 
just  noted.  These  curves  are  in  a  direction  downwards  and 
outwards  toward  the  gingival  edge.  The  result  is  the  formation 
of  that  peculiar  prominence  or  ridge  of  enamel,  itself  not  in- 
creased in  amount,  at  the  cervical  portions,  which  is  so 
characteristically  displayed  in  the  teeth,  (particularly  the 
molars,)  of  the  deciduous  series,  thus  producing  the  appear- 
ance of  great  constriction  at  their  necks.  This  does  not  occur 
in  the  permanent  dentition. 


THE    DENTINE 


6l 


Branches. — As  they  proceed  outwards,  the  tubes  give  off 
exceedingly  fine  subsidiary  tubes.  These  are  branches  which 
somewhat  simulate  those  on  a  twig  of  a  tree.  They  come  off 
alternately  and  laterally  from  the  stem  or  main  trunk,  some- 
times at  right,  sometimes  at  acute  angles  to  it;  they  are  par- 
ticularly abundant  in  the  dentine  of  the  roots,  less  frequent 
in  or  almost  absent  from  that  of  the  crowns,  where  they  are 
chiefly  found  as  the  tube  approaches  its  free  termination.  These 


FIG.  50. — Dentine,  radicular  portion,  showing  branches  of  the  tubes.  D. 
Dentine;  c.  Cementum.  Prepared  and  photographed  by  Dr.  H.  Box,  Royal 
College  of  Dental  Surgeons,  Toronto. 

channels  may  end,  either  in  the  form  of  branches  or  not,  (i) 
in  tiny  spherical  culs-de-sac  near  the  margin  of  the  enamel; 
(ii)  by  anastomoses  with  their  neighbours — "the  terminal 
loops"  of  Kolliker;  (iii)  in  the  interglobular  spaces;  (iv) 
in  the  granular  layer  of  Tomes;  (v)  in  the  cementum;  (vi)  in 
the  enamel-spindles  beyond  the  amelodentinal  junction  or  (vii) 
as  straight  caecal  terminations  in  the  intercolumnar  cement 
substance.  In  the  crown  they  often  divide  dichotomously 
(i.e,,  by  pairs).  These  divisions,  most  commonly  observed 
near  the  pulp  cavity,  are  frequently  bifurcations  which  Kolliker 
has  described  as  being  "repeated  two  to  five  t:mes  or  more, 


62  THE    DENTAL   TISSUES 

so  that  at  length  four,  eight,  sixteen  or  more  canals  may  arise 
from  a  single  one."  He  also  mentions  certain  "ramifications" 
which  would  seem  to  him  to  be  the  sub-divisions  of  the  main 
tubes.  He  says  (op.  cit.  p.  291)  "the  canals,  now  narrower 
after  their  division,  run  close  together  and  nearly  parallel 
towards  the  surface  of  the  dentine;  and,  except  in  the  root, 
just  begin  to  send  out  ramifications  in  the  outer  half  or  outer 
third  of  .their  course.  These  ramifications  appear  in  the  roots, 


P^  r 


FIG.  51. — Terminations  of  the  dentinal   tubes  in  the   spaces  of  the   granular 
layer  of  Tomes.      Prepared  by  grinding.      Unstained.      Magnified  420  times. 


chiefly  as  fine  branches  issuing  from  the  main  tubes,  but  in  the 
crown  bifurcated  terminations  of  them.  In  the  latter  case 
they  are  for  the  most  part  few  in  number:  it  is  otherw  se  in  the 
root,  where  the  branches,  being  generally  close  to  each  other, 
and  passing  off  from  the  canals  at  right  or  acute  angles,  give 
them  sometimes  the  appearance  of  a  feather,  sometimes  of  a 
brush,  the  latter  especially  when  the  branches  are  large  and 
ramify  still  more." 

The  off-shoots,   like  the   main   tubes,   taper   towards   their 
terminations. 


THE    DENTINE  63 

Transverse  sections  of  dentine,  in  which  the  tubes  are  cut 
across,  show  abundant  rounded  piercings  of  the  matrix,  each 
having  a  slightly  modified  boundary  or  wall.  The  boundary 
is  represented  by  a  yellowish  ring — black  or  grey  if  stained 
by  Golgi's  rapid  process — which,  when  unstained,  is  often 
quite  unrecognisable;  but  nevertheless  exists  as  one  of  the 
sheaths  of  Neumann.  The  walls  are  very  minute,  and,  in 
thickness  less  than  the  diameter  of  the  aperture  of  the  tubule. 


FIG.  52. — Dentinal  tubes  in  transverse  section.     Prepared  by  Weil's  process. 
Magnified  800  times. 


Kolliker  gives  a  description  of  and  pictures  (pp.  cit.  p.  291), 
a  transverse  section  through  the  dentine  of  the  roots  of  teeth 
in  which  the  tubes  are  intimately  connected  by  extremely 
numerous  anastomoses.  Probably  it  was  taken  close  to  the 
pulp  surface,  as  there  are  no  indications  in  the  drawing  of  any 
spherical  or  other  termination  of  the  branches. 

The  channel,  in  the  fresh  state,  contains  the  dentinal  fibril 
and  lymph.  The  former  in  transverse  sections  appears  like  a 


THE    DENTAL   TISSUES 


delicate  roundish  dot.1  This  does  not  necessarily  occupy  the 
centre  of  the  canal,  although  it  is  most  probable  that  during 
life  it  fills,  or  very  nearly  fills,  its  entire  length.  It  is  impossible 
to  prepare,  for  histological  purposes,  sections  of  the  hard  and 
soft  tissues  of  teeth  in  combination,  without  altering  their 
normal  characteristics.  Hence  it  seems  reasonable  to  believe 
that  not  only  does  the  protoplasmic  filament  traverse  the  tube 
from  pulp  to  extremity,  but  that  also  it  rarely,  if  ever,  com- 
pletely occludes  it. 

It  is  evident  that  the  contents  of  the  tubules  are  proto- 
plasmic processes  or  fibrils  which  emanate  from  the  odonto- 
blasts  of  the  pulp.  They  represent  their  distal  or  dentinal 


M 


M 


'lOjlQj 

FIG.  53.  FIG.  54. 

FIG.  53. — Diagram  shewing  Tomes*  conception  of  relations  of  (o)  Odontoblasts; 

(F)  Dentinal  fibril;  (T)  Dentinal  tube,  with  its  sheath;  and  (M)  Matrix. 

FIG.  54. — Klein's  conception  of  the  same. 

processes.  E.  Klein,  "Atlas  of  Histology,"  1880,  p.  185, 
considers  that  the  odontoblasts  do  not  furnish  the  dentinal 
fibrils.  He  says:  "I  cannot  find  convincing  evidence  of  the 
odontoblasts  doing  more  than  producing  the  dentine  matrix. 
The  dentinal  fibres  appear  to  me  to  be  derived  solely  from  the 
deeper  layer  of  cells  which  are  wedged  in  between  the  former." 
The  fibrils  themselves  are  soft  structureless  threads,  devoid 
of  a  covering  of  any  kind,  and  continuous  through  all  the  length 
of  the  tubule  and  its  branches.  They  are  bathed  during  life 
with  a  serous  exudation  from  the  surface  of  the  pulp.  This 

1  Bodecker,  "Dentin,  Cement  und  Schmelz,"  in  Heitzmann's  "  Mikroscopische 
Morphologic,"  Vienna,  1883,  describes  the  fibrils  as  angular,  not  round — under 
enormous  magnifications.  He  thinks  they  give  off  tiny  off-shoots  which  run 
into  the  matrix  of  the  dentine  through  the  sheaths  of  Neumann.  The  action 
of  reagents  used  for  fixing  and  hardening  the  fibrils  in  situ  produced  this  effect 
of  angularity.  The  processes  of  cells  in  other  parts  of  the  body  are  never  angular 
in  cross-section. 


THE    DENTINE  65 

exercises,  no  doubt,  a  trophic  influence  upon  them,  and  prevents 
injury,  which  might  occur  if  they  were  brought  into  immediate 
contact  with  the  lining  membrane  of  the  tubule. 

All  authors  are  not  agreed  on  this  elementary  question 
of  their  contents.  Magitot  ("Traite  de  Carie  Dentaire," 
1878),  says  that  "during  life  the  dentinal  canaliculi  contain 
a  colourless  transparent  fluid;"  and  Morgenstern  ("Ueber 
die  Innervation  des  Zahnbeins"  in  "Archiv.  fiir  Anatomic 
urid  Physiologie,"  1896),  declares  he  has  seen  many  nerve 
filaments  in  the  tubes.  "It  is  the  dentinal  canaliculi,"  he 
writes,  "which  for  the  most  part  contain  the  larger  nerve 
filaments."  His  arguments  are  weak  and  valueless,  depend- 
ing as  they  do  on  the  results  obtained  from  the  vagaries  of 
so  uncertain  and  unreliable  a  method  of  staining  as  that  of 
Golgi,  when  applied  to  sections  of  dentine. 

The  matrix  and  tubes  of  dentine  show  marked  translucency 
in  places,  especially  the  roots,  in  senile  and  functionless  teeth. 

(iii)   The  Sheaths  of  Neumann 

After  careful  decalcification  there  remains  a  soft,  mucoid, 
felt-like  mass,  the  organic  part  of  dentine — the  walls  of  the 
tubes.  Highly  elastic  and  slightly  cohesive  to  the  inter- 
mediate matrix,  when  thus  isolated  the  sheaths  look  like 
long  yellow-elastic  connective  tissue-fibres:  but  they  are,  of 
course,  quite  hollow.  They  possess  no  histological  signifi- 
cance. They  were  first  accurately  and  most  fully  described 
by  Neumann  in  I863.1  He  demonstrated  that  all  soft  tissues 
of  the  tooth  having  first  been  removed,  subsequent  macera- 
tion in  boiling  acids,  of  various  strengths  for  varying  periods 
of  time,  led  to  dissolution  of  the  whole  of  the  inorganic  elements, 
and  left  behind  a  tube-like  formation,  which  was  characterised 
by,  and  distinguished  from,  the  dentine  matrix  by  the  peculiar 
property  of  resisting  the  action  of  chemical  substances,  and  by 
great  elasticity,  and  slight  cohesion  with  the  inter-tubular 
material.  Some  attention  has  lately  been  again  given  to  the 

1  "Em  Beitrag  zur  Kenntniss  des  Normalen  Zahnbcin-und  Knochen-gewebes." 
Leipzig. 


66  THE    DENTAL    TISSUES 

question  of  the  existence  or  non-existence  of  these  sheaths;  and 
interest  revived  in  what  seems  a  simple,  but  is,  in  reality, 
a  complex  study.1  Optical  effects  are  so  easily  produced  when 
examining  dentine:  its  collagenous  substance  is  so  hard:  its 
association  with  the  soft  protoplasmic  easily-destructible  soft 
tissues  so  direct  and  complete,  that  it  can  be  no  small  matter  for 
wonder  that  investigators  still  hold  opposite  opinions  which 
give  rise  to  considerable  confusion. 


^ 


FIG.   55. — The  sheaths  of  Neumann.      Prepared  by  decalcification  and  teasing 
out.     Stained  with  borax-carmine.      Magnified  240  times. 


Neumann  affirmed  that  the  tubules  possess  proper  walls. 
He  called  them  "Dental  Sheaths"  ("Zahnschieden")  and  he 
added  that:  "In  the  dental  tubes  are  contained  fibrous  non- 
calcified  processes  of  the  peripheral  pulp-cells  ("Tooth-fibres"). 
In  this  way  was  corroborated  the  original  statement  of  John 
Tomes  in  1856,  in  his  classical  contribution  to  the  Philosoph- 
ical Transactions  of  the  Royal  Society,  entitled  "On  the  presence 
of  fibrils  of  soft-tissue  in  the  dentinal  tubes." 

1  "A_Study  of  the  Minute  Structure  of  Dentine"  by  Dr.  Kanae  Hanazawa, 
Tokyo.  "  The  Dental  Cosmos,"  1917. 


THE    DENTINE  67 

Kolliker,  who  actually  first  discovered  them  by  acid  macera- 
tion, points  out  that  the  apparent  walls  of  the  tubes  in  trans- 
verse sections  are  not  the  real  walls,  but  a  certain  length  of  the 
canals  themselves,  which  appear  as  dark  rings.  If,  however, 
an  edge,  very  narrow  in  width,  and  yellowish  in  colour,  is  seen, 
this  he  regards  as  the  true  wall  ("Mikroscopische  Anatomic," 
Leipzig,  1854). 

Oscar  Romer  denies  in  toto  the  existence  of  these  sheaths 
of  Neumann.  In  his  monograph  already  quoted,  Part  I.  is 
devoted  entirely  to  the  consideration  of  their  presence  or  non- 
presence  in  dentine.  According  to  his  measurements,  they 
are  I/JL  to  2/j,  in  width  at  their  broadest  part.  He  contends 
that  the  contents  correspond  to  the  walls  of  the  tubes;  in  other 
words,  "that  the  odontoblast  processes  (or  dentinal  fibrils), 


FIG.   56. — Diagram  showing  Romer's  conception  of  relations  of  (o)  Odontoblasts; 
(F)  Dentinal  fibril;  and  (M)  Matrix. 


really  correspond  to  Kolliker s  dentinal  tubules,"  are  therefore 
hollow,  and  continue  as,  and  do  not  enter  into  Neumann's 
sheaths.  He  sums  up  his  arguments  with  the  following  asser- 
tions : — 

(a)  The  fibrils  described  and  depicted  by  Tomes  in  1856 
are  no  new  formations,  but  completely  identical  with 
the  dentinal  fibrils  described  by  Kolliker  in  1834,  while 
Tomes'  membrane  of  the  fibrils  corresponds  to  the  wall 
of  the  tubules,  and  to  Neumann's  sheath;  and  the  con- 
tents of  the  fibrils,  described  by  Tomes  as  semi-fluid, 
correspond  to  the  contents  of  the  tubules  described 
as  fluid  by  other  writers. 

(6)  The  dentinal  tubes  assumed  by  Tomes  do  not  correspond 
to  the  dentinal  tubules  of  Kolliker,  but  are  artificially 
produced,  wall-less,  tube-shaped  hollow  spaces  produced 


68  THE    DENTAL    TISSUES 

in  the  matrix  of  dentine  by  decalcincation  and  dissolution, 
spaces  from  which  Kolliker's  tubules  and  Tomes'  tubes 
can  be  easily  isolated. 

(c)  The  odontoblast  processes,  designated  "Tooth-fibres" 
or  "Tomes's  fibres,"  are  not  the  contents  of  Kolliker's 
dentinal  tubules,  but  represent  both  the  sheath  of  Neu- 
mann and  the  contents  together.  Therefore,  the  concep- 
tion of " Tooth  fibres " or  "Tomes's  fibres,"  as  the  contents 
of  Kolliker's  tubules,  must  be  dropped,  and  we  must  con- 
tent ourselves  for  the  present  with  the  original  assumption, 
that  the  contents  of  the  dentinal  tubules  are  a  fluid  or 
semi-fluid  material,  or  one  that  has  not  yet  been  adequately 
investigated. 

And  he  concludes: — "According  to  my  observations,  there  do 
not  exist  in  the  dentinal  substance  any  tubules  other  than  those 
of  Kolliker.  The  dentinal  tubes  of  Tomes  are  only  tube- 
shaped  holes  produced  in  the  dentinal  substance  by  maceration; 
one  cannot  perceive,  even  under  the  strongest  magnifying 
power,  and  even  in  stained  section-preparations  of  normal 
non-carious  dentine — whether  in  transverse,  longitudinal,  or 
diagonal  section — any  intervening  space  whatever,  between 
odontoblast  process  (or  the  dentinal  tubule)  and  the  matrix 
of  the  dentine."  Romer's  observations  are  entirely  faulty 
and  untrustworthy;  for  the  processes  of  cells  in  other  parts  of 
the  body  are  never  hollow — with  the  possible  exception  of  the 
cilia  of  ciliated  columnar  epithelium,  which  are  highly  specalised 
processes  of  the  cells  endowed  with  movement. 

The  various  contradictory  theories  concerning  the  existence 
and  non-existence,  the  walling,  and  the  contents  of  the  dentinal 
tubules  may  be  briefly  mentioned  as  follow : 

(i)  Their  absence  is  affirmed  by  Magitot  (1880). 
(ii)  Their  presence  in  mature  dentine  is  denied  by  Xavier 
Sudduth  (1887),  who  ("American  System  of  Dentistry," 
p.  594),  says:  "The  salts  of  calcium  are  deposited 
around  the  fibrils  of  the  odontoblasts,  and  in  a  certain 
sense,  dentinal  tubuli  may  be  said  to  exist  at  that  time. 
We  may  say  that  this  tissue  is  an  aggregation  of  tubes 
containing  fibrils,  but  in  the  process  of  aggregation  they 


THE    DENTINE  69 

lose  their  identity  as  such,  becoming  cemented  to- 
gether into  a  solid  tissue."  And  further,  "The  fact  that 
dentine  is  not  capable  of  being  broken  up  into  tubes  is, 
in  my  mind,  conclusive  evidence  against  the  theory  of 
the  existence  of  a  dentinal  sheath  per  se  as  the  wall  of  a 
dentinal  tube." 

(iii)  There  are  two  kinds  of  tubules  in  dentine,  one  con- 
taining the  processes  of  the  odontoblasts,  the  other, 
finer,  to  receive  nerve  fibres.  An  unproved  postulate 
of  Franz  Boll,  1868,  "  Untersuchungen  iiber  die  Zahn- 
pulpa"  in  "Archiv  fur  Mikroskopische  Anatomic." 
Bd.  iv. 

(iv)  The  processes  of  the  odontoblasts  (dentinal  fibrils) 
are  Kolliker's  dentinal  tubes.  Lent,  1885,  "Ueber  die 
Entwickelung  des  Zahnbeins  und  des  Schmelzes," 
"Zeitschr.  fur  wissensch.  Zoologie,"  Leipzig. 
(v)  The  sheaths  of  Neumann  are  dependent  on  calcified 
dentine  substance,  because  they  are  invisible  (absent) 
in  the  dento-genetic  zone.  Erwin  Hohl,  1896,  "Beitrag 
zur  Histologie  der  Pulpa  und  des  Dentins"  in  "Archiv 
fur  Anatomie." 

(vi)  The  membrane  of  the  processes  of  the  odontoblasts 
form  the  sheaths  which  run  in  wall-less  tubes.  The 
sheaths  in  situ  are  wider  than  those  artificially  isolated 
by  acids.  Romer,  1899,  op.  cit. 

(vii)  Their  existence  as  separated  structures  is  doubted  by 
Underwood,  "Aids  to  Dental  Anatomy  and  Physi- 
ology," 1902. 

(viii)  The  tubules  have  definite  walls  (sheaths),  and  contain 
Tomes'  dentinal  fibrils, — processes  from  certain  cells 
of  the  pulp.  Tomes  op.  cit.  1914;  as  well  as  many 
other  authors. 

(iv)   The  Inter  globular  Spaces  of  Czermak 

At  varying  distances  below  the  amelo-dentinal  junction  are 
found  in  apparently  sound  as  well  as  in  imperfectly  developed 
dentine  numerous  globular  markings  arranged  in  linear  series, 
and  running  transversely  to  the  dentinal  tubes.  Defective 


7o 


THE    DENTAL   TISSUES 


dentine  exhibits  them  remarkably  well.  They  were  first 
described  by  J.  Czermak  in  1850,  and  designated  by  him  the 
"  interglobular  spaces."  "Beitrag  zur  Mikro-Anatomie  der 
Menschlicher  Zahne." 

As  Tomes  has  pointed  out,  they  are  due  to  an  arrested 
development  of  the  tissue  during  certa  n  early  stages  of  its 
growth,  when,  for  some  cause  or  other,  the  calco-globular 


FIG.   57. — Interglobular  spaces  crossed  by  dentinal  tubes.      Prepared  by  Weil's 
process.      Magnified  240  times. 

masses  have  not  fused,  or  have  only  partially  melted  together. 
The  functions  of  the  lime-bearing  cells  of  the  pulp  have  become 
temporarily  modified,  and  instead  of  the  dentinal  basis-sub- 
stance being  deposited  in  proper  amount  and  regularity — 
making  a  homogeneous  whole — the  calco-globular  masses  have 
remained  unchanged  or  slightly  changed,  and  the  matrix  has 
flowed  around,  and  become,  in  time,  fully  calcified. 

Seen  under  advantageous  circumstances,  e.g.,  in  sections 
which  have  been  carefully  ground  thin,  and  stained  by  Golgi's 
silver  chromate  method,  or  impregnated  with  coloured  collo- 
dion, the  spaces  vary  greatly  in  shape  and  size.  Their  scalloped 
edges  are  made  up  of  the  rounded  or  oval  margins  of  spheres 


THE    DENTINE  7 1 

of  calco-globulin  mutually  pressed  together.  If  these  bodies 
retain  their  rotundity,  the  spaces  have  here  three,  four,  five,  or 
more  concavities  forming  their  outline,  the  semi-lunes  being 
often  dissimilar  in  size  and  shape;  there,  they  have  a  lobulated 
appearance;  while  elsewhere,  by  the  process  of  union  of  two  or 
three  spaces,  they  become  elongated  and  irregular.  In  dia- 
meter they  vary  from  2.5^  to  4.2ju,  or  less. 

As  to  their  contents  they  are  generally  believed  to  hold 
in  their  interiors,  in  the  fresh  state,  soft  protoplasm  which 
fills  them  entirely.  Dentinal  tubules  often  traverse  them. 
Tomes  has  proved  this  by  noting  in  fragments  of  carious  den- 
tine, that  the  tubules  which  cross,  not  only  contain  micro- 
organisms, but  have  themselves  become  occasionally  enlarged. 
The  protoplasm,  under  favourable  conditions,  undergoes  cal- 
cification, and  the  dentine  is  said  to  be  areolated.1 

Dentinal  tubules  may  terminate  in  the  interglobular  spaces. 

In  dried  sections,  they  contain  air,  a  fact  which  is  easily 
demonstrated  by  soaking  thin  slices  of  dentine  in  coloured 
collodion,  which  runs  into  and  fills  every  part.  They  are 
therefore  in  dried  specimens  veritably  "spaces." 

(v)   The  Granular  Layer  of  Tomes 

In  the  radicular  portions  of  teeth,  and  beginning  at  the 
cervical  margin,  is  the  granular  layer.  It  stretches  as  a  fairly 
thick  black  or  grey  band,  round  the  roots,  at  the  periphery  of 
the  dentine  immediately  internal  to  the  cementum.  It  pre- 
sents the  appearance,  under  low  powers,  of  a  line  of  black 
grains  of  sand.  Near  the  neck  of  the  tooth  the  layer  is  narrow, 
but  as  it  reaches  the  apical  foramen,  it  broadens  out  con- 
siderably, and  soon  is  more  pronounced.  This  is  not,  however, 
constant.  The  author  possesses  a  section  in  which  the  rows  of 
interglobular  spaces  and  the  granular  layer  are  coalescent  at 
a  spot  immediately  subjacent  to  the  ending  of  the  enamel 

1  These  areolations  of  dentine  are  most  likely  perfectly  analogous  with  those 
irregularly  shaped  layers  made  up  of  solid  rounded  calcined  bodies  seen  occasion- 
ally near  the  surface  of  the  shafts  of  long  bones,  lying  in  their  osseous  lamina?. 
They  differ,  however,  in  the  fact  that,  whereas  the  former  betray  certain  develop- 
mental defects,  the  latter  mark  various  sites  of  absorption  and  re-deposition  of 
bone. 


72  THE    DENTAL    TISSUES 

at  the  cervical  region;  and  here  the  latter  is  very  broad  and 
marked.     In  some  sections  it  is  hardly  at  all  visible. 

On  closer  examination,  these  multitudinous  dots  assume 
various  irregular  shapes.  Some  are  more  or  less  circular, 
others  oval;  some  triangular,  others  quadrate;  some  clavi- 
form,  others  stellate;  a  granule — in  a  word — represents  a 
compromise  between  an  interglobular  space  and  a  lacuna  in 
hyperplasic  cementum. 


G 


FIG.  58. — The  granular  layer  of  Tomes.  Prepared  by  grinding  and  staining 
with  coloured  collodion.  Magnified  240  times.  D.  Dentine;  c.  Cementum; 
G.  Granular  layer. 

Many  instances  are  noted  where  the  terminations  of  the 
dentinal  tubules  end  in  these  tiny  spaces;  and  when  canaliculi 
seem  to  led  from  them,  they  can  be  traced  to  one  of  the  endings 
of  a  tubule. 

Approaching  the  apex  of  the  root,  the  spaces  increase  greatly 
in  numbers,  and  are  much  larger  and  more  irregular.  Occa- 
sionally, a  large  spindle-shaped  lacuna  may  be  found.  The 
layer  is  situated  in  a  matrix  of  dentine  which  is  distinctly 
granular;  though  the  term  "granular  layer"  refers  obviously 
to  the  spaces. 


THE    DENTINE  73 

Their  contents,  according  to  Bodecker,  are  soft  protoplasm 
which  is  in  connection  with  the  contents  of  the  tubules  on  one 
side,  and  the  canaliculi  of  the  cemental  lacunae  (when  they 
exist)  on  the  other.  It  would  seem,  however,  that  it  is  by  no 
means  easy  to  prove  this  assertion.  The  granular  layer  is 
stained  with  the  utmost  difficulty  by  the  action  of  carmine  or 
any  of  the  other  basic,  acid,  or  aniline  dyes.  It  is  more  likely 
to  be  beyond  the  pale  of  nutrition. 

Bounding  the  granular  layer  externally  is  a  very  narrow 
strip  of  homogeneous  dentine:  then  comes  a  dark  line — it  is 
nothing  more  than  that — which  forms  the  point  of  demarca- 
tion between  dentine  and  cementum.  The  homogeneous  zone 
and  this  line  are  devoid  of  any  structure  whatever. 


FlG.    59. — Schreger's  lines  in  dentine.      From  the  ivory  of  the  tusk  of  a  walrus. 
Prepared  by  grinding.      Unstained.      Magnified  45  times.      Cf.  Fig.  26. 

(vi)  Schreger's  Lines 

These,  sometimes  seen  in  horizontal  sections  of  dentine, 
must  not  be  confounded  with  Schreger's  lines  in  enamel. 
Many  of  the  dentinal  tubes  as  they  course  outwards  form  the 
artificial  appearance  of  bands,  through  the  primary  curvatures 
passing  in  the  same  direction.  Thus,  Schreger's  lines  are 


74 


THE    DENTAL   TISSUES 


merely  markings  which,  running  parallel  to  the  external  edge 
of  dentine,  are  produced  by  the  coincidence  of  the  primary 
curvatures  of  the  tubules  (see  Fig.  60). 

They  are  well — perhaps  best — exhibited  in  sections  of  the 
ivory  of  the  tusk  of  the  walrus,  where  they  appear  to  be  due 
to  sudden  short  bends  or  twists  of  the  primary  curvatures,  oc- 
curring at  identical  places  in  their  lengths.  The  effect  under 
low  powers  is  a  much  striated  character  of  the  tissue. 


FIG.   60. — Same  as  the  preceding.      Magnified  420  times.     Cj.  Fig.  27. 

(vii)  The  Contour  Lines  of  Owen1 

comprise  (i)  Schreger's  lines  in  dentine,  and  also  (ii)  rows  of 
so-called  "dentinal  cells."  Under  low  powers  these  rows 
resemble  lines,  particularly  in  human  molars  and  in  the  teeth 
of  Cetacea,  and  it  is  to  them  that  he  refers  when  he  describes 
them  as  "contour  lines."  On  page  460,  he  says,  "Both  the 
primary  and  secondary  curves  of  adjacent  tubes  are  parallel; 
and  occasionally  the  tubes  make  a  short  bend  along  a  line 
parallel  with  the  outer  contour  of  the  crown,  giving  rise  to 
the  appearance  which  may  be  called  "contour  lines,"  the  par- 

1O\ven:  " Odontography,"  1840. 


THE    DENTINE 


75 


allelism  of  the  entire  tubes  being  affected  only  by  the  amount 
of  divergence  in  radiating  from  the  pulp  cavity."  Again 
(p.  464),  "These  lines  are  not  equally  conspicuous  in  every 
tooth;  I  have  usually  found  them  most  so  in  the  molars  of 
the  human  subject,  where  without  being  regularly  equidis- 
tant, they  have  presented  intervals  of  about  one  hundredth  of 


FIG.  61. — Contour  lines  of  Owen  in  dentine.  Vertical  section  of  Human 
molar.  Decalcified.  Stained  with  Ehrlich's  acid  hasmatoxylene.  Magnified 
40  times.  L.  Owen's  lines,  running  in  a  transverse  direction. 

an  inch,  commencing  at  thrice  that  distance  from  the  periphery 
of  the  dentine." 

With  regard  to  the  last-named  histological  formation,  i.e., 
the  "dentinal  cells,"  Owen  remarks,  "In  many  teeth,  more- 
over, and  especially  in  the  tusks  of  the  elephant,  the  secondary 
branches  of  the  dentinal  tubes  dilate  into  intertubular  cells 
along  lines,  which  in  like  manner  are  parallel  to  the  coronal 


76  THE   DENTAL   TISSUES 

contour  of  the  tooth;  hence  another  cause  of  the  appearance 
of  concentric  lamellae,  and  of  the  actual  decomposition  of 
such  teeth  into  super-imposed  lamelliform  cones."  These 
dentinal  or  "  calcigerous  cells,"  as  this  distinguished  author 
also  designates  them,  form  many  layers  having  a  certain 
amount  of  parallelism  with  the  contour  of  the  pulp  cavity. 
He  described  them  first  in  a  Report  to  the  British  Asso- 
ciation in  1838  (vol.  vii.,  p.  144).  They  are  not  animal 
cells  in  the  modern  acceptance  of  the  term,  but  in  the  inter- 
spaces of  the  tubes  they  include  a  "tubular  structure."  "The 
intertubular  space  is  not  cellular,  but  clear  and  structureless." 
To-day,  histologists  would  prefer  to  think  of  them  as  repre- 
senting merely  the  calcified  outlines  of  what  might  have  been 
interglobular  spaces.  Owen's  contour  lines  were  seen  by 
Salter,1  who,  however,  prefers  to  call  them  "incremental  lines," 
as  indicating  more  accurately  the  manner  in  which  the  tooth 
substance  is  built  up. 

(viii)  Lamella  or  Lamina 

Occasionally,  though  seldom,  vertical  sections  of  roots  or 
human  molars,  when  ground,  reveal  very  clearly  certain 
markings  in  the  periphery  of  the  dentine.  Ranged  at  right 
angles  to  the  tubules,  and  running  concentrically  with  the 
pulp  chamber,  these  short  straight  strips  are  very  numerous 
in  some  sections,  sharply  defined  and  bright  when  unstained, 
of  variable  length,  and  cross  the  tubes  near  their  extremities. 
They  are  non-pathological  in  origin,  and  are  not  artificially 
made  by  the  action  of  reagents.  Most  probably  they  re- 
present marks  of  stratification  during  the  development  of  the 
tissue. 

A  second  class  of  laminae  is  often  seen  in  the  matrix  of 
mature  dentine  when  decalcified  in  hydrochloric  acid,  and 
stained  with  haematoxylene.  Vertical-transverse  (labio- 
lingual)  sections  of  molars,  show  over  the  cornua  of  the  pulp, 
regularly  arranged  faint  shadings,  separated  by  brighter 
less-coloured  lines;  and  in  the  cervical  and  radicular  regions, 
rounded  dots  (which  are  probably  the  same  as  Owen's  dentinal 

1  "Dental  Pathology  and  Surgery,"  page  10,  1874. 


THE    DENTINE  77 

cells1)  of  darker  colour  near  the  pulp,  and  near  the  cementum 
long  looped  lines  running  in  the  direction  of  the  tubes.  These 
long  lines  or  laminae  are  joined  at  their  distal  ends  by  delicate 
arcuate  markings,  the  concavities  of  which  always  look  to- 
wards the  pulp. 

Thus,  lamellae  in  dentine  include  two  groups:  the  former, 
short,  tube-like,  straight;  the  latter,  long  wavy  bands  and 
spherical  shadows,  and  lines  joined  by  an  arch. 

These  lamina?  are  not  due  to  staining,  nor  are  they  optical 
illusions.  The  first  group  obtains  in  natural  conditions;  while 
the  others  are  evidently  rendered  more  apparent  by  decalcifica- 
tion,  and  more  striking  by  staining.  They  both  certainly 
indicate  the  manner  in  which  calcine  deposition  has  taken 
place. 

F.  J.  Bennett,2  in  a  paper  on  "  Certain  points  connected  with 
the  Structure  of  Dentine;"  has  described  laminae  in  dentine 
which  has  been  acted  upon,  for  some  length  of  time,  by  glyc- 
erine. In  certain  longitudinal  sections  the  dentine  bordering 
the  margin  of  the  pulp  cavity  "presented  a  ringed  appearance, 
and  was  slightly  laminated."  This  was  due  to  "the  dentinal 
tubes,  in  this  situation,  having  lost  their  surrounding  inter- 
tubular  tissue,  which  left  them  clearly  defined;  but  this  removal 
of  the  matrix  had  not  completely  freed  them.  Their  course 
appeared  to  be  interrupted,  at  regular  intervals,  by  layers  of 
membrane  having  a  general  direction  parallel  to  the  surface 
of  the  pulp.  The  layers  of  membrane  (laminae)  bore  a  general 
resemblance  to  that  seen  in  interglobular  dentine;  in  this  case, 
however,  circular  apertures  and  not  solid  globules  occupied 
the  surface  of  the  membrane.  Oval  spaces  were  also  found 
between  the  layers  of  membrane."  Bennett  put  forward  the 
following  hypotheses,  as  being  the  explanation  of  such 
phenomena : 

(a)  The  laminae  might  represent  a  part  of  the  matrix  of 
dentine,  which,  possessing  a  greater  power  of  resisting  the 
solvent  action  of  glycerine  than  the  rest,  represents  a  new 
transitional  stage  or  phase  in  its  calcification;  or 

1  Owen's  "Odontography."     PI.  xcv.  fig.  2,  also  cxiii.,  fig.  2,  and  cxix.,  fig.  i. 
2  Trans.  Odonto.  Soc.  of  Gt.  Britain,  Vol.  xxi.,  p.  6,  1889. 


78  THE    DENTAL    TISSUES 

(b)  Unequal  expansion  or  contraction  of  certain  parts  of 
the  matrix,  producing  separation  of  the  layers;  or 

(c)  Evidences  of  cell  structure  in  the  matrix. 

SECONDARY   DENTINE 

Secondary  dentine  is  a  physiological  product.  In  the 
strictest  sense  of  the  term,  it  should  be  used  to  designate 
every  form  of  new  tissue  deposited  in  the  substance  or  on 
the  surface  of  the  pulp,  which  occurs  after  full  development 
of  that  organ  and  of  the  dentine.  It  has  been  hitherto  used, 
however,  for  describing  both  physiological  and  pathological 
conditions.  Salter's1  patient  and  remarkable  investigations 
in  that  particular  portion  of  dental  pathology  which  deals 
with  degenerative  changes  in  the  dental  pulp,  led  him  to 
classify  all  forms  of  dentinal  deposition  as  secondary  dentine, 
and  in  a  sense  this  was  perfectly  correct.  But  the  term  seems 
to  require  a  more  definite  meaning;  for  he  describes  under 
this  one  heading  three  kinds: — "Dentine  of  repair,"  "dentine 
excrescence,"  and  "osteo-dentine"  or  "intrinsic  calcification." 

It  would  be  more  correct  in  modern  days,  since  so  many 
varieties  of  pathological  dentine  have  become  known,  to 
restrict  the  expression  entirely  to  physiologically  constructed 
dentine  found,  e.g.  (i)  in  the  incisive  margins  of  the  persistently 
growing  teeth  of  Rodentia,  etc.,  in  Man  (ii)  in  the  accompani- 
ments of  old  age,  or  (iii)  the  deposits  sometimes  found  in  long- 
retained  deciduous  teeth.  Senile  teeth  constantly  possess  a 
complete  mass  of  secondary  dentine  occluding  the  pulp  cavity, 
the  occurrence  of  this  having  been  brought  about  in  a  physio- 
logical manner.  As  a  non-pathological  result  of  an  active  state 
of  the  pulp,  secondary  dentine  may  lastly  be  associated  with 
(iv)  attrition,  abrasion  or  fracture  of  the  teeth,  when  not 
complicated  by  caries  of  enamel  or  dentine. 

1  "Dental  Pathology  and  Surgery,''  chaps,  xi.  and  xii.,  1874. 


CHAPTER  V 
THE  CEMENTUM 

MICROSCOPICAL    ELEMENTS:    (i)    Matrix;    (ii)    Incremental    lines;    (iii) 
Perforating  fibres. 

GENERAL   CHARACTERISTICS 

Definition.- — The  thin  hard  substance1  situated  immediately 
external  to  the  dentine  of  the  roots  of  teeth  of  Man  and  many 
animals. 

Origin.- — It  is  a  product  of  the  osteoblasts  of  the  perio- 
dontal  (alveolo-dental)  membrane,  i.e.,  the  thin  inner  layer  of 
the  dental  capsule. 

Distribution. — In  the  great  class  Mammalia  cementum  or 
crusta  petrosa — a  former  appellation — forms  the  cortex  of  the 
radicular  dentine:  but  also  in  the  ox,  horse,  elephant,  capy- 
bara,  and  other  animals,  it  not  only  unites  the  roots  of  teeth, 
but  before  attrition  has  taken  place,  exists  as  the  coronal 
integument. 

In  Man,  it  normally  measures,  in  width,  from  175^  to  250^. 

It  is  rarely  found  in  the  teeth  of  Pisces  and  Reptilia;  and  is 
normally  absent  from  the  roots  of  anchylosed  teeth.  Ovarian 
teeth  also  do  not  always  possess  it. 

Macroscopical  Appearances. — Whitish  -  yellow  in  colour, 
smooth,  dull,  line  of  junction  with  enamel  pronounced_and 
darker  than  rest  of  cementum. 

HISTOLOGY 

The  structures  calling  for  special  microscopical  attention  in 
this  the  least  important  of  all  the  hard  dental  tissues  of  man, 
are,  (i)  Matrix,  or  basis-substances;  (ii)  Incremental  lines; 
and  (iii)  Perforating  canals  and  fibres. 

1  The  chemical  composition  of  human  cementum  is  unknown. 

79 


8o 


THE    DENTAL    TISSUES 


(i)  The  Matrix 


The  matrix  or  basis-substance  makes  up  the  greater  part 
of  the  tissue.  It  extends  as  a  narrow  non-vascular  lamina 
round  the  roots  of  teeth  external  to  the  homogeneous  layer  of 
dentine,  beginning  at  the  cervical  region  and  covering  over 
the  apices  of  the  roots,  though  like  the  dentine  it  is  discon- 
tinuous at  the  apical  foramina.  Its  relationship  to  enamel  has 
already  been  alluded  to;  its  relationship  to  dentine  is  such  as 


am  Cementum 


Dentine 


FIG.   62. — Granular   appearance   of  cemental   matrix.      Magnified    1,000  times. 
(Photomicrograph  by  Norman  Broomell.) 

to  make  it  difficult,  if  not  at  times  impossible,  to  determine 
where  the  one  begins  and  the  other  ends.  Often  no  sharp 
line  of  demarcation — as  in  the  case  of  enamel  and  dentine — 
exists. 

The  general  appearance  of  this  tissue  varies  very  much — 
thus  it  may  be  hyaline,  finely  granular,  or  even  made  up  of 
bodies  of  an  amorphous  type. 

It  is  capable  at  times  of  being  stained,  especially  at  its  outer- 
most part.  Normal  cemental  matrix  in  young  and  old  sub- 
jects is  therefore  nearly  structureless.  Roots  of  simple  teeth 


THE    CEMENTUM  8 1 

unaffected  by  morbid  processes  show  this  thin  layer,  which 
maintains  the  same  degree  of  thinness  throughout  its  whole 
extent.  In  the  case  of  bi-rooted  premolars  or  molars,  how- 
ever, there  is  a  tendency  for  it  to  become  slightly  thicker  on 
their  alveolar  or  inner  aspects.  In  old  age  it  is  somewhat 
thicker  (see  Chapter  III,  Vol.  II). 

But  in  every  section  of  cementum,  faint  shadings  of  a  slightly 
different  refractive  index  to  other  parts  of  the  tissue  can,  on 


FlG.  63. — Same  as  preceding.     Magnified  420  times.     D.  Dentine;  c.  Cementum. 

careful  examination,  be  clearly  differentiated.  Normally  they 
are  but  feebly  revealed.  These  shadings  are  arranged  in  two 
ways :  The  more  pronounced  run  parallel  to  the  periphery,  and 
without  doubt  represent  immature  incremental  lines:  the  others, 
which  are  very  numerous,  cross  the  first-named  at  right  angles. 
Both  classes  can  be  observed  in  vertical  as  well  as  horizontal 
preparations  (Fig.  66). 

In  thus  describing  the  minute  organisation  of  this  tissue, 
the  author  would  like  to  emphasize  the  fact,  that  in  his  opinion, 
formed  as  the  result  of  the  examination  of  many  sections, 
the  cementum  of  the  teeth  of  man  is  usually  free  from  lacunae 


82 


THE    DENTAL    TISSUES 


FIG.  64. — Incremental   lines.     Prepared  by  grinding.     Unstained.     Magnified 

400  times. 


H  C 

FIG.  65. — Perforating  canals  and  fibres  in  cementum.  Prepared  by  grinding. 
Stained  with  chloride  of  gold.  Magnified  40  times.  C.  Cementum;  H.  The 
homogeneous  layer  of  dentine;  D.  Dentine. 


THE    CEMENTUM 


FIG.  66. — Cementum.  Prepared  as  in  last  figure.  Incremental  lines  and 
homogeneous  layer  well  defined.  Magnified  400  times.  L.  Incremental  lines; 
H.  Homogeneous  layer. 


FIG.   67. — Longitudinal  lamellae  of  cementum,   showing  numerous  varicosities. 
Magnified  1,000  times.      (Photomicrograph   by   Norman   Broomell ) 


84 


THE    DENTAL    TISSUES 


and  canaliculi,  being  nothing  more  nor  less  than  a  dense,  solid, 
nearly  homogeneous  band  of  calcined  basis-substance,  ex- 
tending round  the  roots.  The  teeth  of  monkeys  and  sheep 
(root  portions)  have  been  inspected  microscopically;  and 
here,  as  in  man,  it  exists  as  a  thin  strip  almost  devoid  of  his- 
tological  elements,  such  as  those  characteristic  of  bone.  In 
the  opossum  and  certain  other  marsupials,  however,  a  thick 
layer  of  cementum  is  found  sufficiently  often  to  be  practically  a 


FIG.  68. — Striated  cementum  from  radicular  region  of  tooth,  near  apex,  to 
show  the  complex  character  of  the  thicker  tissue,  viz.:  "The  longitudinal  striae, 
transverse  fibres,  cement-corpuscles  and  zones  of  apparently  -unbroken  granular 
matrix."  Magnified  100  times.  (Photomicrograph  by  Norman  Broomell.) 


characteristic  of  this  class.  The  reader  is  referred  to  page  no 
in  this  connection.  This  lack  of  lacunae  in  normal  cementum 
has  also  been  observed  by  Otto  Walkhoff  (op.  cit.  pp.  142,  143) 
and  figured  by  him  in  Plates  v.  and  ix.:  both  statement  and 
photographs  having  been  brought  to  the  notice  of  the  writer 
since  the  preceding  lines  were  penned. 

But  one  of  the  after-effects  of  a  morbid  change  or  a  series 
of  morbid  changes  in  the  alveolo-dental  periosteum — however 


THE    CEMENTUM  85 

slight,  is  the  stimulation  of  the  otherwise  quiescent  osteo- 
blasts,  to  deposit  osseous  material  on  the  periphery  of  the  tissue: 
and  lacunas  are  then  formed,  imprisoning  the  osteogenetic 
cells.  A  single  lacuna  may  not  infrequently  be  observed 
situated  near  the  granular  layer  of  Tomes;  and  this  would 


FIG.  69. — To   show  partial   calcification    of   the   incremental   lines.      Magnified 
1,000  times.      (Photomicrograph  by  Norman  Broomell.) 

indicate  abnormal  processes  going  on  about  the  time  the 
earliest  deposited  cementum  is  completed.  There  is,  there- 
fore, under  healthy  conditions,  no  chain  of  living  matter 
joining  the  pulp  to  the  periodontal  membrane. 

(ii)  Incremental  Lines 

represent  the  marks  of  stratification  during  development. 
They  look  like  sinuous  unbroken  lines  placed  in  a  fairly  regular 


86  THE   DENTAL    TISSUES 

and  uniform  manner  one  over  the  other.  Sharply  marked 
off  from  the  rest  of  the  matrix,  at  times,  and  running  in  a 
parallel  direction  to  the  long  axis  of  the  root,  they  give  rise  to 
a  lamellated  structure  (Fig.  67). 

In  young  cementum  the  lamellae  correspond  in  number  over 
all  portions  of  the  root,  the  only  difference  being  that  they  are 


FIG.  70. — Transverse  section  of  an  adult  premolar  near  apex,  to  show  the 
varying  disposition  of  the  lamellas.  The  incremental  lines  follow  the  surface  of 
the  dentine.  "As  the  centre  of  the  area  is  approached,  this  regularity  is  much 
interfered  with,  some  of  the  lamellae  being  discontinued,  others  greatly  thickened, 
while  the  field,  taken  in  its  entirety,  suggests  anything  but  regularity  in  the  lay- 
ing down  of  the  different  strata.  Magnified  60  times.  A.  Granular  layer  of 
Tomes.  (Photomicrograph  by  Norman  Broomell.) 

much  thinner  at  the  cervical  than  at  the  apical  region:  in 
adult  cementum  their  width  is  greater,  and  they  are  usually 
more  numerous  in  the  latter  than  the  former  situation1  (Norman 
Broomell). 

The  term  " Incremental  lines"  was  introduced  by  Salter, 
("Dental  Pathology  and  Surgery,"  1874),  and  includes  the 

1  "The  Histology  of  Cementum."  The  Dental  Cosmos,  Vol.  xl.,  p.  706,  1898: 
also  Broomell  and  Fischelis'  "Anatomy  and  Histology  of  the  Mouth  and  Teeth," 
p.  351, 1917. 


THE    CEMEXTUM  87 

laminations  sometimes  found  in  enamel  (but  not  the  brown 
striae  of  Retzius,  or  Schreger's  lines),  the  contour  lines  of  Owen 
in  dentine,  and  the  layers  of  stratification  in  cementum. 

Stohr  ("Text-book  of  Histology,"  Wurtzburg,  1914)  says  that 
"  Cementum  contains  typical  bone  cells  enclosed  in  large  lacuna? 
which  connect  with  one  another  through  canaliculi.  In  young 
teeth  Haversian  canals  are  absent,  but  in  old  teeth  they  occur 
in  the  outer  layers  near  the  apex  of  the  root."  These  are  alto- 
gether erroneous  statements.  And  Sir  Ernest  Schafer  ("The 
Essentials  of  Histology,"  1916)  figures  on  page  303  a  drawing 
after  Sobotta,  which  gives  an  entirely  false  impression  of  the 
structure  of  normal  cementum.  There  are  no  lacunae  in  the 
normal  tissue:  the  illustration  is  that  of  hyperplasic  cementum. 

(iii)  Perforating  Canals  and  Fibres 

In  close  juxtaposition  to  the  band  of  homogeneous  tissue 
which  borders  the  dentine,  and  running  at  right  or  acute  angles 
to  it,  in  adult  normal  cementum,  there  can  be  commonly  seen 
thick  bundles  of  connective  tissue  fibres  and  broad  irregular 
canals.  In  this  way  the  homogeneous  layer  is  bounded  inter- 
nally by  the  granular  layer,  externally  by  groups  of  perforating 
canals  and  fibres.  The  former  are  few  and  irregularly  curved 
in  an  outward  direction,  and  may  occasionally  extend  half- 
way through  the  thickness  of  the  cementum.  The  author  has 
found  some  of  them  supplied  writh  tiny  filamentous  branches. 
The  latter  on  high  magnification  are  seen,  in  sections  prepared 
by  Weil's  process,  to  consist  of  myriads  of  bundles  of  blackish 
strands.  They  are  short  and  thick,  and  remind  the  observer 
of  the  odontogenetic  fibres  of  dentine  matrix.  Their  outer 
extremities  may  enter  the  canaliculi  (Fig.  71). 

Black  considered  them,  and  seemingly  with  sound  scientific 
reasonableness,  to  be  the  calcified  or  semi-calcified  remains 
of  the  "principal  fibres,"  of  the  periodontal  membrane. 

Sharpey's  fibres,  penetrating  from  without,  may  be  noted 
in  some  sections  of  cementum  where  the  hard  and  soft  parts 
have  been  prepared  and  preserved  in  situ.  They  are  very 
short  straight  or  slightly  curved  bundles  of  fibrils,  the  main 


88 


THE   DENTAL   TISSUES 
H 


G 


FIG.  71.- — Longitudinal  section  of  cementum.  Prepared  by  Weil's  process. 
Shows  the  perforating  canals  and  fibres.  Magnified  420  times,  c.  Cementum; 
G.  Granular  layer;  H.  Homogeneous  layer;  D.  Dentine. 


FIG.   72. — Sharpey's    fibres   of   cementum.      Magnified   800    times.      Unstained. 
c.  Cementum  slightly  hyperplasic. 


THE    CEMENTUM 


89 


characters  of  which  agree  with  white  fibrous  tissue,  while 
some  may  be  of  the  nature  of  elastic  tissue.  They  are  identical 
with  the  perforating  fibres  in  the  lamella?  of  bone.  In  cemen- 
tum  they  occupy  the  interiors  of  slightly  truncated  canals. 


Dentimi 
tubes 


FIG.  73. — Perforating  fibres  passing  from  the  outer  margin  of  the  first- 
deposited  cementum  outwards  "until  the  next  incremental  line  is  reached,  at 
which  point  they  gradually  disappear,  but  recur  in  the  succeeding  lamelhc." 
Magnified  1,000  times.  A.  Primary  or  oldest  layer  of  cementum.  (Photomicro- 
graph by  Norman  Broomell.) 

As  will  be  seen,  Sharpey's  fibres  are  entirely  distinct  struc- 
tures compared  to  the  perforating  fibres  described  above. 

Normal  cementum  is  non-vascular;  but  there  would  seem 
to  be,  in  the  majority  of  cases,  fine  protoplasmic  fibrils  which 
traverse  the  boundary  line  between  dentine  and  cementum. 

Norman  Broomell,  in  the  excellent  study  already  men- 
tioned, would  recognise  in  the  tissue  under  consideration 


9o 


THE    DENTAL   TISSUES 


three  zones  or  layers,  not  always  discernible  but  fairly  con- 
stant. The  inner,  first-formed,  is  granular,  unbroken,  and 
continuous  with  the  granular  layer;  the  intermediate  con- 
tains many  lacunae;  and  the  outer  or  youngest  exhibits  many 
sinuous  incremental  lines.  As  the  tissue  becomes  more  fully 
calcified  the  lacunas  disappear,  and  the  zone  possesses  many 


Homoge- 
neous 
layer  of 
dentine 


FIG.  74. — Fibres  passing  in  a  direction  almost  parallel  to  the  surface,  and 
towards  the  apex  of  the  root.  Magnified  300  times.  (Photomicrograph  by 
Norman  Broomell.) 


of  the  histological  characters  of  the  oldest  layer.  Tomes 
describes  this  last  layer  in  thick  cementum  as  a  "glassy  film, 
denser  than  the  subjacent  portions,"  and  considers  it  closely 
similar  to  the  globular  formations  characteristic  of  dentine  in 
an  early  stage  of  development. 

Underwood,  in  "Aids  to  Dental  Anatomy  and  Physiology," 
p.  49,  1902,  said:  "The  outermost  layer  of  cementum  is  struc- 
tureless: .  .  .  when  young,  globular  forms  may  be  traced 
in  its  substance." 


THE    CEMENTUM 

A 


Granular  j^^BB 

layer  ^™ 


Dentine 


FIG.  75. — Fibres  springing  from  the  granular  layer  of  Tomes,  at  regular 
intervals,  and  penetrating  the  cementum  at  right  angles  to  the  incremental  lines. 
Magnified  500  times.  A.  The  circumferential  fibres  of  Broomell.  (Photomicro- 
graph by  Norman  Broomell.) 


FIG.   76. — Structureless  cementum  of  a  deciduous  tooth.      Prepared  by  grinding. 
Unstained.      Magnified  200  times.      D.  Dentine;  c.  Cementum. 


Q2  THE    DENTAL   TISSUES 

It  is,  however,  perfectly  obvious  that  he  still  inclined  to  the 
belief  that  normally  this  tissue  contains  lacunas  and  cana- 
liculi. 

Cementum  in  deciduous  and  supernumerary  teeth  is 
relatively  thinner  than  that  of  the  permanent  series.  It  is 
nothing  more  than  a  very  narrow,  structureless  band  (Fig. 
76). 


CHAPTER  VI 

STRUCTURAL  MODIFICATIONS  OF  THE  ENAMEL, 
DENTINE  AND  CEMENTUM 

MICROSCOPICAL  ELEMENTS  IN  THE  ENAMEL  OF:  (i)  Rodentia;  (ii) 
Sirenia.  (iii)  TUBULAR  ENAMEL,  (iv)  PLICI-DENTINE  ;  (v)  VASO- 
DENTINE;  and  (vi)  Os TEO -DENTINE.  CEMENTUM. 

Students  of  comparative  anatomy  need  not  be  reminded 
that  the  subject  is  full  of  interest  with  regard  to  the  modified 
forms  of  teeth,  not  only  in  number  and  shape  but  also  in  size 
and  function.  It  is  not  surprising,  then,  that  the  minute 
structure  of  the  masticatory  organs  of  the  lower  vertebrates 
not  infrequently  differs  very  remarkably  from  that  of  man. 
As  was  hinted  in  Chapter  III.,  enamel  may  be  found,  in  some 
instances,  clear  and  structureless,  in  others,  presenting  a  most 
complicated  pattern.  Here  will  be  briefly  considered  the 
chief  variations  in  the  histology  of  the  enamel,  dentine  and 
cementum  met  with  in  the  vertebrates.  Tomes'  "  Manual  of 
Dental  Anatomy"  will  ever  remain  the  standard  work  on  the 
subject,  and  to  this  and  to  Sir  Richard  Owen's  "Odontography" 
readers  are  referred  for  elaborated  details. 

> 

ATYPAL   VARIATIONS    OF    ENAMEL 

Among  Mammalia,  the  Order  Rodentia  supplies  many  in- 
stances of  modification  in  structure  of  this  tissue.  These  varia- 
tions may  be  a  provision  on  the  part  of  nature  to  render 
the  free  surface  and  incisive  margin  of  the  teeth  particularly 
strong.  Taking  the  Families  in  their  proper  anatomical  order, 
brief  reference  can  only  be  given  to  the  histology  of  the  enamel 
of  (i)  the  Muridce,  mice,  rats,  &c. ;  (ii)  Castoridcz,  beavers; 

93 


94 


THE   DENTAL   TISSUES 


(iii)  Soricida,  squirrels;  (iv)  Hystricidce,  porcupines;  and  (v) 
Leporidce,  rabbits  and  hares.  In  Rodentia,  generally  speaking, 
the  large  incisors  are  frequently  pigmented  a  deep  orange 
colour.  According  to  Tomes,  the  colour  is  situated  in  the 
substance  of  the  enamel  itself. 

Enamel  invests  the  anterior  and  lateral  aspects  of  the  teeth 
and  is  thicker  in  the  former  than  in  the  latter  situation. 


FIG.  77. — Vertical  section  of  a  persistently  growing  scalpriform  tooth  of  a 
rodent.  Prepared  by  grinding.  Stained  with  borax-carmine.  Magnified  240 
times.  Shows  striation  of  enamel  rods.  E.  Enamel;  D.  Dentine;  A.  Amelo- 
dentinal  junction. 


(i)  In  the  rat  the  straight  columns  are  arranged  in  a  parallel 
direction,  and  are  placed  at  an  acute  angle  with  the  surface  of 
the  dentine.  This  is  seen  in  the  accompanying  photograph 
(Fig.  77).  Each  rod  is  not  only  very  striated  but  is  alse  deeply 
indented,  and  by  making  serrations  with  its  neighbours 
renders  the  tissue  remarkably  dense  and  difficult  to  fracture. 

(ii)  The  enamel  of  the  beaver  exhibits  a  lattice-like  arrange- 
ment of  the  rods.  Longitudinally  cut,  the  enamel  rods  are 
"inclined  upward  towards  the  apex  of  the  tooth,  at  an  angle 
of  60  deg.,  then,  after  passing  through  about  half  the  thickness 


STRUCTURAL  MODIFICATIONS  OF  THE  HARD  TISSUES  95 

of  the  enamel,  they  turn  up  abruptly  again,  so  that  they  are 
approaching  parallelism  with  the  dentine,  here  making  an 
angle  little  less  than  30  deg.  with  it.  It  follows  from  this 
that  no  transverse  section  can  show  very  plainly  the  direction 
of  the  rods  in  both  parts  of  their  course.  The  most  instruc- 
tive transverse  section  is  one  cut  parallel  with  the  layers  near 
to  the  dentine;  this  will  plainly  show  the  successive  layers 
passing  to  the  right  and  to  the  left  just  as  in  the  squirrel; 
but  the  yet-more-inclined  fibres  of  the  outer  half  of  the  enamel 

will  then  be  cut  across  obliquely As  regards  the 

decussation  of  the  rods  of  ultimate  layers,  it  is  similar  to  that  of 
the  Soricidce,  but  it  differs  in  the  laminae  being  slightly  flexu- 
ous  instead  of  pursuing  perfectly  straight  lines"  (Tomes). 

(iii)  An  apparent  division  into  inner  and  outer  portions 
is  exhibited  in  the  enamel  of  the  squirrel.  Here,  the  rods 
are  continuous  through  all  the  thickness  of  the  tissue,  but, 
running  in  different  directions  when  viewed  either  vertically 
or  horizontally,  produce  a  complex  pattern. 

"In  the  former  they  leave  the  dentine  at  right  angles  to 
its  surface,  and  after  traversing  two-thirds  of  the  enamel, 
suddenly  bend,  and  form  an  angle  of  45  deg.  with  their  original 
course:  in  the  latter,  they  are  arranged  in  horizontal  layers, 
each  layer  a  single  column  in  thickness.  In  alternate  layers 
the  rods  pass  to  the  right  and  to  the  left,  crossing  those  of 
the  next  layer  at  right  angles,  and  thus  making  a  pattern  of 
squares  in  the  inner  two-thirds  of  the  enamel.  In  the  outer 
third,  where  the  rods  bend  abruptly  upwards,  those  of  super- 
imposed layers  no  longer  pass  ;n  opposite  directions,  but  are 
all  parallel;  in  fact,  no  longer  admit  of  distinction  into  alter- 
nate laminae"  (Tomes). 

(iv)  Individually,  flexuous  rods  are  found  in  the  enamel  of 
the  porcupine,  the  courses  of  which  are  not  confined  to  one  plane. 
At  the  periphery  of  the  tooth  the  rods  run  in  a  parallel  direction. 

(v)  Parallel,  slightly  curved  enamel  columns  are  constant 
in  the  teeth  of  hares. 

In  the  Order  Sirenia,-oi  which  the  manatee  is  an  example, 
the 'enamel  rods  run  in  a  perfectly  straight  course,  and  are  not 
flexuous.  This  is  therefore  a  very  simple  type. 


g6  THE    DENTAL   TISSUES 

Simpler  variations  still  are  found  in  Pisces.  Some  Families, 
e.g.,  eel,  hake,  etc.,  have  a  homogeneous  type  of  enamel  which 
exists  as  a  tiny  free  structureless  point  on  the  dentine.  The 
majority  of  fishes,  however,  probably  possess  a  system  of 
tubes  which  pass  either  partially  or  wholly  through  the  enamel. 


GENERAL   CHARACTERISTICS 

Definition. — As  the  expression  implies,  the  enamel,  instead 
of  being  a  solid  mass  of  rods  and  basis-substance,  presents  a 
tubular  structure. 

Origin. — The  tubes  are  produced  through  the  failure  of 
calcification  of  the  central  zones  of  the  rods  formed  by  the 
ameloblasts  of  the  enamel  organ. 

Distribution. — A  class  characteristic  of  Marsupials  (except 
the  wombat),  but  found  also  in  some  examples  of  Pisces,  e.g., 
Sargus,  barbel,  porbeagle  shark,  and  certain  Insectivora  (So- 
ricidce)  and  Rodentia,  such  as  jerboa,  etc. 

HISTOLOGY 

The  chief  point  of  interest  is  the  presence  of  a  system  of 
tubular  canals  in  the  substance  of  the  tissue.  These  may  be 
very  extensive  and  numerous,  or  very  short  and  few;  and  be 
confined  to  the  inner  or  cortical  aspects  of  the  enamel  or  in 
its  intermediate  portion^ 

It  has  already  been  'shown  that  in  human  enamel  dentinal 
tubes  often  cross  the  amelo-dentinal  junction,  to  end  either 
ccecally  or  else  in  the  enamel-spindles.  But  in  addition  to 
these,  comparative  anatomy  furnishes  many  instances  where 
other  tubes  occur.  Dentinal  tubes  pass  across  the  boundary 
and  run  into  the  enamel  in  marsupials  (e.g.,  kangaroo). 

In  many  fishes,  the  passage  of  these  tubes  from  the  dentine 
takes  place,  but  the  canals  grow  smaller  in  calibre  as  they 
approach  the  enamel  cortex,  which,  however,  they  do  not 
reach.  Tomes  describes  and  figures  (op.  cit.  p.  56)  enamel 


STRUCTURAL  MODIFICATIONS  OF  THE  HARD  TISSUES 


97 


from  the  tooth  of  a  fossil  shark  in  which  the  tubes  pierce  both 
the  inner  and  outer  zones.  In  Sargus  Ovis,  and  Cestracion 
(Heterodontis]  they  likewise  penetrate  from  the  surface. 

The  tubes  are  found  in  the  longitudinal  axes  of  the  enamel 
rods,  not  in  the  basis-substance;  and  their  courses  are  generally 


FIG.  78. — Sagittal  section  of  incisor-like  tooth  of  Sargus  Ovis,  showing  tubular 
enamel.  Prepared  by  grinding.  Unstained.  Magnified  about  10  times.  E. 
Enamel;  D.  Dentine. 

fairly*  .straight  and  parallel.  In  Sargus,  nevertheless,  after 
peripheral  penetrations  and  running  at  right  angles'^ with 
the*surface,  they  suddenly  bend  at  an  obtuse  angle  with  their 
course  (see  Fig.  78). 

It  is  difficult  to  offer  a  satisfactory  explanation  of  the  pres- 


98  THE    DENTAL    TISSUES 

ence  of  these  enamel  tubes,  but  the  opinion  expressed  by 
Tomes  is,  no  doubt,  correct. 

Thus  (p.  59)  he  writes:  "If  all  enamel,  in  its  development, 
passes  through  a  tubular  stage,  then  these  are  merely  arrests 
of  complete  development  and  perpetuations  of  a  stage  which 
is  transitory  in  placental  mammals." 

It  is  probable  that  tubular  enamel  is  atavistic. 


FIG.   79.- — Same  as  preceding.      Magnified  240  times. 

Paul's  views  are  not  in  accord  with  those  of  Tomes.  In 
an  article  in  The  Dental  Record,  p.  496,  1896,  this  author 
observed: 

"If  we  admit  the  general  principle  that  all  spaces  or  tubes 
in  enamel  are  between  and  not  within  the  rods,  then  the 
structure  of  genuine  tubular  enamel  seems  less  difficult  to 
understand.  It  is  clear  that  any  imperfect  approximation 
of  enamel  cells  must  leave  spaces  between  the  rods  which 
can  only  be  filled  with  an  indefinite  intercellular  substance, 
or  possibly  by  further  prolongations  of  dentine  matrix,  and 
in  neither  case  is  it  likely  that  such  intercolumnar  matter 
would^become  calcified;  because  on  the  one  hand,  it  is  too 


STRUCTURAL  MODIFICATIONS  OF  THE  HARD  TISSUES 


99 


far  removed  from  the  influence  of  the  odontoblasts,  and  on 
the  other,  because  the  calcifying  energy  of  the  ameloblasts 
is  almost  entirely  expended  upon  their  own  internal  petri- 
faction. I  would  therefore  suggest  that  tubular  enamel  is 
an  enamel  in  which  there  is  an  excessive  amount  of  inter- 
cellular substance  only  imperfectly  calcified,  and  much  as  it 
looks  like  tubular  dentine,  it  is  really  formed  on  an  exactly 


4      fc      -  r 

*  / 


FIG.   80. — Transverse  section  of  a  rostral  tooth  of  Pristis.     Prepared  by  grinding. 
Stained  with  coloured  collodion.      Magnified  about  10  times. 

opposite  plan.  The  one  is  a  negative  and  the  other  a  posi- 
tive picture.  In  dentine  the  cells  occupy  the  tubes,  and  the 
intercellular  substance  becomes  the  solid  calcined  matter; 
in  enamel  the  tubes  are  represented  by  the  intercellular  sub- 
stance, whilst  the  cells  become  the  solid  calcined  matter." 

But  it  must  be  confessed  that  Paul's  remarks  seem  hardly 
quite  apposite  in  this  connection,  based  as  they  are  on  the 
probably  incorrect  hypothesis  that  odontoblasts  form  dentine 
matrix.  The  syllogism  he  uses  is  faulty,  inasmuch  as  the 
premises  are  not  generally  accepted,  and  are  open  to  a  dif- 


100  THE    DENTAL   TISSUES 

ferent  interpretation.  In  his  studies  of  marsupial  enamel, 
Howard  Mummery's  opinion  coincides  with  those  of  Paul, 
who  investigated  the  subject  from  the  point  of  using  the  enamel 
of  man.  His  conclusions  (Phil.  Trans.  1914)  are  that  "The 
prisms  (sic)  are  the  first  portions  of  the  enamel  which  undergo 
calcification,  that  these  prisms  (sic)  are  arranged  in  layers  corre- 
sponding to  the  rows  of  ameloblasts  cells  and  that  the  spaces 
between  the  layers  are  calcified  subsequently  and  cement  the 
tissue  together." 

VARIETIES    OF   DENTINE 

Tomes  has  classified  Mammalian  dentine  as  ortho-den- 
tine (Hard,  or  unvascular  dentine,  sufficiently  described  in 
Chapter  IV.),  plici-dentine,  vaso-dentine,  and  osteo-dentine. 
This  is  considerably  more  correct  than  that  found  in  the  writings 
of  Owen,  who  somewhat  confuses  the  two  last-named  varieties. 
Thus  the  older  palaeontologist  described  vaso-dentine  as  being 
composed  of  coarse  channels  containing  cells,  vessels,  and  nerves 
of  the  pulp — obviously  the  osteo-dentine  of  the  latter  author. 
By  limiting  the  expression  vaso-dentine  to  those  forms  in  which 
blood-vessels  only  permeate  the  dentine,  Tomes  has  cleared 
away  many  conflicting  conceptions. 

Plici-dentine 

Definition. — "An  ordinary  dentine  with  its  surface  folded  up 
and  wrinkled  into  a  greater  or  less  degree  of  complexity" 
(Tomes). 

Histologically  considered,  the  dentine  is  hard,  and  unchan- 
nelled  except  by  tubes  which  radiate,  as  usual,  more  or  less 
at  right  angles  to  the  pulp  cavity. 

If  a  pulp  chamber  be  merely  indented  externally,  or  if 
portions  of  the  dentine  are  somewhat  invaginated,  or  the  pulp 
itself,  instead  of  being  simple  in  outline,  has  several  prolonga- 
tions, no  longer  does  a  cylindrical  pulp  cavity  result,  but  one 
with  folded  outlines. 

This  obtains  in  the  teeth  of  the  Selache  maxima  (Basking 
shark),  or  Ichthyosaurus. 


STRUCTURAL  MODIFICATIONS  OF  THE  HARD  TISSUES          IOI 

vr 


FIG.  81. — Transverse  section  near  base  of  tooth  of  Anarrhicas  lupus.  Shows 
the  plicated  outlines  of  the  dentine.  Magnified  45  times.  From  a  specimen  in 
the  collection  of  Sidney  Spokes. 


FIG.  82. — A  form  of  Plici-dentine.  Transverse  section  of  tooth  of  an  extinct 
crocodile  (Telcosaurus),  Prepared  by  grinding.  Unstained.  Magnified  240 
times. 


IO2  THE    DENTAL    TISSUES 

In  Lepidosteus  the  upper  part  of  the  tooth  consists  of  a  simple, 
single  pulp  chamber,  with  plicated  walls,  while  at  its  base  there 
are  several  pulp  chambers  running  longitudinally,  and  variable 
in  size,  each  always  having  radiating  dentinal  tubes.  The 
peripheral  pulp  cavities  run  in  straight  lines  in  a  centrifugal 
direction.  And  so  also  in  Anarrhicas  lupus  (Fig.  81). 

If  these  straight  lines  become  twisted  or  curved  or  branched, 
a  much  more  complex  pattern  is  produced,  as  in  the  extinct 


FIG.   83. — The  same  as  the  preceding.     Longitudinal  section.      Magnified  240 

times. 


reptiles  Labyrinthodon,   Leptognathus,    and   Dendrodus   Bipor- 
catus;  also  an  extinct  Crocodile  Teleo-saurus. 

Many  teeth  are  composed  of  groups  of  vertical  denticles 
or  primary  pulp  canals  with  radiating  dentinal  tubules.  The 
periphery  of  each  system  occasionally  blends  almost  imper- 
ceptibly with  those  of  neighbouring  denticles.  Thus  a  regular 
pattern  is  seen  in  both  horizontal  and  vertical  sections.  The 
teeth  of  the  rostrum  of  Pristis,  of  an  extinct  hippopotamus, 
Myliobates,  Zygobates,  and  others  reveal  this.  In  the  first 
condition  each  dentinal  system  is  permeated  with  fibrils  from 


STRUCTURAL  MODIFICATIONS  OF  THE  HARD  TISSUES         103 

the  central  pulp.     The  dentine  is  hard  and  unvascular,  but  not 
plicated. 

Vaso-dentine 

Another  variety  of   this   dental   tissue,   in   which,   broadly 
speaking,  there  are  no  tubules  as  such,  is  vaso-dentine.     As 


FIG.  84. — Sagittal  section  of  an  intermaxillary  tooth  of  Anarrhicas  lupus 
Prepared  by  grinding.  Unstained.  Magnified  about  10  times.  The  mass  of 
tooth  is  occupied  by  vaso-dentine. 

the  term  implies,  it  is  a  vascular  dentine.  Extending  outwards 
through  the  matrix  is  a  series  of  moderately  sized  canals  or 
channels  of  nearly  uniform  calibre  throughout,  each  filled 
with  a  capillary  from  the  pulp. 


THE    DENTAL    TISSUES 

The  channels  run  in  the  same  direction  as  the  tubes  in  hard 
dentine — that  is,  radially.  A  little  below  the  free  surface  of 
the  tooth  their  distal  extremities  are  formed  by  loops,  the 
convexities  of  which  are  outwards.  Dried  sections  some- 
times show  thorn-like  processes,  running  laterally  from  the 
vascular  canals  (see  Fig.  85). 


FIG.  85. — Vertical  section  of  tooth  of  Merlucius  vulgaris  (Hake).  Prepared 
by  Weil's  process,  with  the  substitution  of  Golgi's  method  of  staining.  Magni- 
fied 250  times.  Shows  the  vascular  channels  in  the  dentine,  with'their  so-called 
"thorns,"  and  the  laminated  matrix  of  the  dentine. 


The  matrix  of  the  dentine  itself  is  slightly  laminated. 

Vaso-dentines  are  found  in  many  fishes — hake,  cod,  Sargus, 
flounder,  haddock,  &c.,  in  the  former  of  which  the  canals  are 
numerous,  in  the  latter  scanty.  The  dentine  of  the  first-named 
is  tubeless.  The  teeth  of  manatee  and  Megatherium  possess 
vascular  canals  as  a  normal  characteristic. 

Osteo-dentine 

In  its  general  histological  configuration,  osteo-dentine 
closely  approximates  to  that  of  compact  bone,  but  the  inter- 
stitial and  peripheric  lamellae  are  wanting.  Its  irregular 


STRUCTURAL  MODIFICATIONS  OF  THE  HARD  TISSUES         105 

spaces  are  analogous  with  the  medullary  canals  of  compact  bone. 
They  contain,  however,  in  this  case,  not  medullary  tissue,  but 


FIG.  86. — Vertical    section    of    base    of    tooth    of    Carcharias.     Osteo-dentine. 
Magnified  50  times. 


pulp  with  round  osteoblastic  cells  lining  the  walls  in  young 
developing  specimens. 


io6 


THE   DENTAL   TISSUES 


Osteo-dentine  is  found  in  the  teeth  of  fishes,  of  which  it  may 
form  the  whole  or  part,  as  in  the  photomicrograph  (Fig.  86). 

In  typical  instances,  when  longitudinally  cut,  it  is  made  up 
of  more  or  less  parallel  trabeculas,  which  extend  through  the 


FIG.  87. — Longitudinal  section  of  ankylosed  tooth  of  Esox  lucius  (Pike). 
Prepared  by  the  Author's  process.  Stained  with  Ehrlich's  acid  haematoxylene. 
Shows  osteo-dentine.  The  full  growth  of  the  osteo-dentine  is  incomplete,  a 
few  elastic  rods  remaining  in  the  centre  of  the  tooth.  Magnified  about  10  times. 
A.  Apex  of  tooth  composed  like  the  periphery  of  the  dentine;  B.  Bone  of  attach- 
ment; E.  Elastic  rods,  or  uncalcified  trabeculae;  p.  Pulp  in  situ;  M.  Soft  tissues  of 
Jhe  mouth. 

substance  of  the  tooth,  traversing  the  pulp  tissue  and  dividing 
it  into  great  numbers  of  pulp  cavities.  There  is  no  very 
regular  tube  system,  otherwise  the  result  of  this  sub-division 


STRUCTURAL  MODIFICATIONS  OF  THE  HARD  TISSUES        107 

into  minor  pulp  cavities  would  be  a  flat  form  of  plici-dentine 
in  which  the  denticles  are  placed  side  by  side  in  a  regular 
and  uniform  manner. 

In  the  osseous  matrix  lacunae  are  sometimes  found,  and  the 


FIG.  88. — Vertical  section  of  tooth  of  Rsox  Indus.  Prepared  by  decalci- 
fication.  Pulp  tissue  not  retained  in  situ.  Stained  with  borax-carmine.  Mag- 
nified 40  times,  o.  Osteo-dentine;  B.  Bone  of  attachment. 

dentine  is  more  or  less  permeated  by  minute  canaliculi.  Many 
variations  from  this  type  exist.  The  structure  of  the  teeth  of 
Lamna  (Porbeagle  shark)  may  be  cited  as  an  example.  Tomes 
(op.  cit.  p.  99)  describes  it  as  follows:  "In  an  osteo-dentine  me- 
dullary canals  of  varying  size  run,  with  a  direction,  roughly 
speaking,  parallel  to  the  long  axis  of  the  tooth,  anastomosing 


108  THE    DENTAL    TISSUES 

with  one  another;  and  from  their  sides  wavy  bundles  of  fine 
tubes  radiate  but  do  not  run  far;  that  is  to  say,  its  dentinal 
tubes  do  not  radiate  from  any  one  central  pulp  chamber,  but 
from  an  indefinitely  large  number  of  canals." 

Recent  Classification  of  the  Varieties  of  Dentine 

Rose  has  recently  attempted  a  new  classification  of  Dentine, 
and  his  communications  to  dental  science,  in  these  as  in  other 
matters,  are  always  interesting.  Thus  he  distinguishes: — 

(i)      Pure  or  Ortho-dentine,  a  term  suggested  by  von  Kupffer, 

(ii)    "Trabecular,"  or  rod-like  dentine, 

(iii)    Osteoid  dentine, 

(iv)    Bone  dentine. 

(i)  Pure  dentine  is  a  hard  tissue  with  a  smooth  surface,  of 
unilateral  growth,  being  developed  under  an  epithelial  sheath 
or  enamel  organ. 

This  includes  the  following  sub-divisions: — 

(a)  Tubular    dentine,    i.e.,    normal    tissue    containing    the 
canals  for  the  reception  of  protoplasmic  cell  processes, 

(b)  Vitro-dentine,  i.e.,   tubeless  and  structureless,    with  no 
protoplasmic  filaments  whatever, 

(c)  Vaso-dentine,  i.e.,  containing  blood-vessels. 

(ii)  Trabecular  dentine,  corresponding  to  the  "osteo-dentine" 
of  Tomes,  is  a  new  term  introduced  by  Rose,  who  defines  it  as 
"a  hard  tissue  with  numerous  short  protoplasmic-bearing 
dentinal  canals,  capable  of  increase  of  growth  in  all  directions, 
but  not  growing  immediately  beneath,  or  in  dependence  upon 
an  epithelial  sheath." 

This  variety  is  probably  formed  similarly  to  intra-mem- 
branous  ossification  of  bone.  Thus,  in  the  interior  of  the 
pulp  cavity,  at  an  early  period  of  development,  arise  rod-like 
tracts  of  closely  aggregated  round  cells.  Within  these  tracts 
or  columns,  the  first  rudiments  of  structureless  dentine  are 
laid  down  exactly  after  the  manner  of  the  formation  of  the 
first  layers  of  compact  or  cancellous  bone.  Single  columns 
grow  and  increase  in  length  and  diameter.  They  thicken  at 
the  expense  of  the  pulp  tissue,  become  fused  in  places,  and  ex- 


STRUCTURAL  MODIFICATIONS  OF  THE  HARD  TISSUES        IOQ 

hibit  fine-tubed  dentinal  systems.  Ultimately  with  the  com- 
pletion of  the  growth  of  the  tooth,  instead  of  there  being 
one  pulp  cavity,  there  are  many  wide  tubular  canals  containing 
pulp  tissue  radiating  in  every  case  in  a  centrifugal  manner. 

E 


FIG.  89. — Vertical  section  of  the  cervical  region  of  a  molar  tooth  of  Didelphys 
Virginiana  (Opossum).  Prepared  by  grinding.  Unstained.  Magnified  45 
times.  D.  Dentine;  E.  Enamel;  c.  Normal  lacunated  cementum. 

The  first  formed  parts  of  the  rods  are  structureless,  and  these 
are  designated  by  this  author  as  Vitro-trabecular  dentine. 

(iii)  Osteoid  dentine  is  a  hard  tissue  growing  in  all  directions ; 
contains  no  protoplasmic  enclosures;  sometimes  forms  pure 
bone  tissue  and  sometimes  trabecular  dentine. 

(iv)  Bone  dentine,  or  Osteo-dentine,  is  a  transitional  form, 
between  bone  on  the  one  hand  and  dentine  on  the  other; 


IIO  THE    DENTAL    TISSUES 

contains   both   bone    corpuscles    and    dentinal    tubules,    each 
carrying  a  protoplasmic  fibril. 

MODIFICATIONS    OF    CEMENTUM 

Little  need  be  recorded  about  this.  It  is  sufficient  here  to 
point  out  that  the  normal  cementum  of  some  of  the  Marsupial 
mammals  (e.g.,  the  opossum,  see  Fig.  89),  does  contain  promi- 
nent well-shaped  lacunae  and  canaliculi.  Not  only  are  the 
spaces  of  fairly  uniform  size,  and  the  canaliculi  of  regular  calibre 
and  length,  but  the  arrangement  in  layers  or  series  is  regularly 
parallel.  Deposition  of  the  tissue  with  inclusion  of  cemental 
corpuscles  has,  doubtless,  proceeded  without  deviations  from 
the  original  and  earliest  formed  layer.  The  cementum,  there- 
fore, forms  naturally  a  thick  coating  to  the  roots  of  the  teeth, 
and  comparison  with  the  lacunated  hyperplasic  cementum 
of  the  teeth  of  man  cannot  fail  to  have  a  striking  and  convincing 
effect  on  the  mind  of  the  astute  and  experienced  observer. 


CHAPTER  VII 
THE  DENTAL  PULP 

MICROSCOPICAL  ELEMENTS: — (i)  Odontoblasts;  (ii)  Pulp  cells  proper;  (iii) 
Fibrous  stroma;  (iv)  Basal  layer  of  Weil;  (v)  Arteries,  Veins,  and 
Capillaries;  (vi)  and  Nerves. 

GENERAL    CHARACTERISTICS 

Definition. — The  soft,  vascular,  and  sentient  organ  which 
occupies  the  central  portions  of  teeth,  being  naturally  bounded, 
on  all  sides,  by  dentine,  which  thus  constitutes  its  cavity. 

Origin. — In  Man  and  Mammalia  it  is  the  ultimate  forma- 
tion of  the  dentine  papilla,  which  is  itself  derived  from  the 
stomodoeal  parietal  mesoderm  (somatopleur). 

Distribution. — All  the  calcified  teeth  of  fishes,  reptiles,  and 
mammals  have  pulps. 

Macroscopical  Appearances. — A  soft,  thin,  flattened,  whitish 
organ,  with,  occasionally,  lines  of  pink  running  in  a  longitu- 
dinal direction  if  removed  from  its  bony  cavity  before  post- 
mortem changes  occur. 

Its  measurements  in  upper  permanent  adult  teeth  are  as 
follows : — 

Greatest  average  width,  sagittally  and  midway  between 
apex  of  root  and  incisive  or  occlusal  edge:  First  incisors,  1.5 
mm.;  canines,  2.5  mm.;  first  premolars,  3.5  mm.;  second  pre- 
molars,  3.8  mm.;  and  molars,  5  mm. 

Greatest  average  length:  First  incisors,  19  mm.;  canines, 
19.5 .  mm.  (in  a  coronal  direction,  23  mm.) ;  first  premolars, 
1,7  mm.;  second  premolars,  15  mm.;  molars  about  15  mm.; 
third  molars,  11.5  mm. 


112 


THE   DENTAL   TISSUES 


m 


fl 

/i     •'  •'/... 


Mi/ 


FIG.  90. — Longitudinal  section  through  the  cornual  region  of  a  young  adult 
molar,  the  dentogenetic  zone  of  which  is  on  the  point  of  calcification.  The  pulp 
is  in  situ.  Prepared  by  the  Author's  process.  Stained  with  Ehrlich's  acid 
hasmatoxylene.  Magnified  80  times.  D.  Dentine;  p.  Pulp  tissue  in  cornu  of 
tooth;  D.Z.  Dentogenetic  zone;  o.  Odontoblasts;  B.L.  Basal  layer  of  Weil;  B. 
Blood-vessels;  N.  Nerve  bundles. 


THE    DENTAL   PULP 


PIG.  91. — Transverse  section  of  an  adult  canine,  with  the  pulp  in  situ.1 
Prepared  by  the  Author's  process.  Stained  with  rubine.  Magnified^  times. 
D.  Dentine;  p.  Pulp  tissue  proper;  Oj.  O2.  O3.  Odontoblast  layer;  A.  Artery; 
V.  Vein;  M.  Myelinic  nerve  bundle. 

xThe  narrowest  diameter  of  the  pulp  in  the  section  of  which  Fig.  91  is  a  photo- 
micrograph, measured  1.5  mm.;  the  widest  diameter  3.35  mm. 


THE   DENTAL   TISSUES 


For  purposes  of  description  it  is  advisable  and  convenient 
to  arbitrarily  divide  the  pulp  as  well  as  the  pulp  chamber 
into  the  (i)  coronal  region — the  most  distal  portion  which 


FIG.  92. — Similar  to  the  preceding  figure,  but  stained  with  Ehrlich's  acid 
haematoxylene.  Magnified  4*5  times.  B.B  B.  Blood-vessels  in  the  basal  layer 
of  Weil. 


projects  into  the  crown  of  the  tooth;  (ii)  the  cornual  region 
indicating  one  of  the  pointed  or  rounded  extremities  of  the 
coronal  region,  (iii)  the  cervical;  and  (iv)  the  radicular  regions — 
that  is,  at  the  neck  and  in  the  roots  of  teeth  respectively. 


THE   DENTAL  PULP  115 

HISTOLOGY 

The  dental  pulp  is  a  delicate  connective  tissue1  consisting 
of  ramified  cells  imbedded  in  a  slightly  fibrous  stroma  and 
granular  transparent  basis  substance,  and  is  plentifully  sup- 
plied with  blood-vessels  and  nerves. 

Examined  microscopically  the  several  parts  of  the  dental 
pulp  of  man  exhibit  objects  of  profound  interest  and  impor- 
tance— of  interest  because  so  many  debatable  and  debated 
theories  circle  around  the  cells  and  nerves,  and  of  importance 
because  on  its  integrity  depends  the  life-history  of  the  tooth. 
To  systematically  study  them,  the  subject  may  be  divided 
into  descriptions  of  (A)  its  cellular  elements,  (B)  its  connective 
tissue  stroma  or  framework,  (C)  its  vascular  supply,  and  (D)  its 
nervous  system. 


The  Cellular  Elements 

The  cells  of  the  dental  pulp  fall  naturally  into  two  classes: 
of  these  the  former  is  the  more  important  when  full  growth 
of  the  organ  has  taken  place;  the  second  during  its  develop- 
mental periods.  A  cursory  examination  of  an  adolescent  or 
adult  pulp  shows  that  two  kinds  of  cells  stand  out  clearly 
distinct  from  each  other — the  peripheral  prominent  layer, 
the  so-called  odontoblasts,  and  the  central,  smaller,  less  con- 
spicuous pulp  cells.  The  latter  should  be  termed  "Odonto- 
blasts," inasmuch  as  it  is  their  function  to  build  the  matrix 
of  dentine;  while  the  former  might  be  known  as  "pulp  cor- 
puscles," signifying  different  work.  See  footnote  on  page  50, 
also  the  Appendix  (page  327). 

As  bearing  upon  this  point  the  statement  of  Rose  may  be 
recalled.  He  says  (loc.  cit.}:  "The  odontoblasts  of  pure 
dentine  have,  like  the  formative  cells  of  'trabecular'  dentine, 
quite  the  appearance  of  osteoblasts.  If  one  wishes  further  to 
distinguish  odontoblasts  from  osteoblasts,  and  chooses  not  to 

1  It  is  said  to  be  similar  to  the  jelly-like  connective  tissue  of  the  early  embryo, 
which  in  the  case  of  the  umbilical  cord  persists,  and  is  called  the  jelly  of  Wharton. 


Il6  THE   DENTAL   TISSUES 

make  use  ot  the  commonly  employed  term  'scleroblasts' 
introduced  by  von  Klaatsh,  new  and  concise  definitions  must 
be  introduced.  It  would  be  commendable  in  the  future  to 
define  only  those  dentine-forming  cells  that  range  themselves 
along  an  epithelial  sheath  as  'odontoblasts,'  quite  indif- 
ferently, whether  one  refers  to  multangular  cells  below  or  cy- 
lindrical cells  above.  Hence  the  word  'odontoblasts'  belongs 
only  to  those  formative  cells  of  true  dentine.  The  formative 
cells  of  'trabecular'  dentine  and  bone  tissues,  which  have  never 
had  any  connection  with  an  epithelial  sheath  should,  on  the 
other  hand,  be  defined  as  osteoblasts." 


(i)   The  Cells  of  the  Membrana  Eboris  of  Kdlliker  or  the 
Odontoblasts 


All  along  the  periphery  of  young  or  mature  pulps,  arranged 
like  a  palisade  in  a  single  row  two  or  three  cells  deep,  is  a  col- 
lection of  large,  columnar  epitheloid  cells.  This  layer  is  most 
marked  at  the  coronal  portion  of  the  pulp,  and  becomes  appre- 
ciably less  distinct  at  the  cervical  portion,  while  in  the  region  of 
the  root  it  is  practically  invisible.  It  is  most  clearly  seen 
in  the  developing  teeth  of  kittens  and  other  embryos,  as  well  as 
in  complete  sagittal  longitudinal  sections  of  young  and  adult 
human  pulps,  although  in  the  latter  the  columnar  character  of 
the  layer  has  disappeared.  In  transverse  sections,  too,  this 
layer  is  visible,  and  it  is  not  difficult  to  say  with  accuracy  from 
which  portion  of  the  pulp  the  particular  section  has  been  taken. 
A  closer  inspection  reveals  the  fact  that  the  membrana  eboris 
is  composed  of  cells — the  so-called  odontoblasts,  a  term  sug- 
gested by  Waldeyer  in  1870,  and  generally  adopted  since  that 
time.  In  young  pulps  it  consists  of  a  single  row  of  cells;  in 
adult  specimens  several  rows.  These  cells  are  of  the  utmost 
interest  and  moment.  They  will  be  described  with  regard  to 
shape,  size,  relationships,  structure,  processes,  and  analogies. 

(a)  An  odontoblast,  generally  speaking,  in  its  very  earliest 
phase  of  development,  is  represented  by  a  large  oval  nucleus, 


THE    DENTAL   PULP 


JI7 


•  < *  V   V '%'  •  •*.  ••>  „  » 

*4     -        PV    * 

:. ;-:  v^v 

?-f        -v  -»  >^ 

FIG.  93. — The    structure    of    the   pulp   tissue.     Prepared   by  Weil's  process 
Magnified  250  times. 


/as      ?v. 

;  \ 

%-  v^' 

.H        Uv     IK 


A 


•vf.V 


J  i  Jw*« 

-  •;..'>" 


1 


vI^.A-^ 

iJ: 1*— *^ 

FIG.  94, — Same   as   the  preceding.     Prepared  by  the  Author's  process.     Mag- 
nified 250  times,     c.  A  Capillary. 


n8 


FIG.  95. — Odontoblasts  on  the  surface  of  the  pulp.  Prepared  by  fixing  and 
hardening  in  formalin  and  alcohol,  and  cutting  on  an  ether-freezing  microtome. 
Stained  with  chloride  of  gold.  Magnified  250  times.  To  show  the  enormous 
length  of  the  dentinal  processes  of  the  cells. 


FIG.  96.- 


-  Young  odontoblasts  from  a  developing  tooth  germ, 
times.     O.  Odontoblasts. 


Magnified  250 


THE    DENTAL    PULP 


devoid  of  visible  protoplasm  (Paul).1  It  may  be  recognised 
without  difficulty,  when  about  one-fourth  its  normal  size.  "It 
then  consists  of  a  large  oval  nucleus  situated  at  its  extreme 
base,  with  a  short  pyramid  of  protoplasm  reaching  towards  the 
surface,  and  displacing  the  fibres  of  the  surface  pulp  cells  on 
either  side.  At  this  time  it  possesses  no  dentinal  fibre,  merely 
ending  in  a  blunt  point,  though  no  doubt  some  delicate  invisible 
protoplasmic  processes  are  given  off." 

Later  on,  but  while  still  young,  and  during  its  period  of 
greatest  activity,  an  odontoblast  is  a  large  bipolar,  nucleated, 
epitheloid  cell,  more  or  less  columnar  in  shape.  This  varies 
considerably  in  the  same  specimen,  and  ranges  from  that  of 
a  mere  thin  cord  with  bulbar  terminations  to  that  of  a  pear 
or  banana,  as  Underwood2  has  likened  it.  Many  cells  are 
carrot-shaped,  many  caudate.  Some  are  short  and  thick,  some 
long  and  thin;  some  have,  as  is  well  known,  square  dentinal  ends, 
others  rounded  extremities.  But  it  would  appear  that  those 
found  in  fully  grown  pulps  are  more  or  less  pyriform  in  shape, 
while  those  in  older  specimens  are  reduced  often  to  a  thin  fibrous 
bundle.  A  point  worthy  of  notice  is  the  fact  that  cells  in  the 
same  plane  —  the  same  section  —  differ  much  in  conformation. 
Where  the  pulp  is  constricted  or  flattened  laterally,  there  the 
odontoblasts  are  thick  and  short;  in  the  place  where  the  pulp 
is  broadest,  however,  they  are  long  and  thin.  Moreover,  in  the 
latter  situation,  in  adult  pulps,  they  have  enlarged  extremities, 
that  near  the  dentine  sometimes  presenting  a  stellate  appear- 
ance, with  the  processes  leaving  the  cell  from  the  points  of  the 
star.  Most  probably  this  has  been  occasioned  by  shrinkage  of 
the  cells  through  the  action  of  reagents.  Often  this  dentinal 
extremity  is  triangular,  often  rounded.  The  central  portion 
or  body  of  the  cell  is  very  considerably  attenuated  and  cordlike 
(see  Fig.  97). 

In  teeth  having  cylindrical  pulp  cavities  this  diversity  in 
shape  is  scarcely  appreciable,  and  probably  does  not  exist. 

It  may  be  said  that  the  same  remarks  apply  also  to  the  pulps 
of  fully  formed  deciduous  teeth. 

1  "A  Contribution  to  the  Histological  Study  of  Dentine."     Trans.  Odonto.  Soc. 
of  Great  Britain,  p.  129,  1899. 

2  "Aids  to  Dental  Anatomy  and  Physiology,"  p.  25,  1902. 


THE    DENTAL    TISSUES 


FiG.  97. — Similar  to  Fig.  91.  The  odontoblasts  marked  O?  in  that  photo- 
graph. Magnified  750  times.  To  show  the  peripheral  processes  extending,,into 
the  dentinal  tubes  as  the  dentinal  fibrils. 


FIG.  98. — Similar   to    Fig.    91.     The   odontoblasts   marked   O3   in   that  photo- 
graph.     Magnified  750  times. 


THE    DENTAL   PULP  121 

An  odontoblast  is  said  to  have  no  limiting  membrane. 

Pathological  conditions,  such  as  inflammation,  suppura- 
tion, or  calcareous  degeneration  of  the  pulp  do  not  seem,  at 
first,  to  affect  the  shape  of  the  odontoblasts:  this  rule  obtains 
in  all  normal  and  abnormal  examples.  But  later  their  forms 
become  profoundly  altered. 

(/3)  With  regard  to  size,  odontoblasts  vary  considerably,  the 
coronal  cells  being  larger  and  more  marked  than  the  radicular 
cells  of  the  pulp.  This  change  in  size  corresponds  in  a  measure 
to  the  length  and  width  of  the  tubules,  with  which  they  are 
closely  associated.  The  largest  cells  in  an  embryonic  tooth- 
germ — viz.,  those  under  that  part  of  the  dentine  which  is  cov- 
ered by  enamel,  and  called,  for  the  sake  of  brevity,  the  coronal 
part  of  the  pulp — have  a  diameter  of  10  to  15/4,  and  if  they  be 
compared  to  adult  cells  in  the  same  situation,  the  latter  will 
be  found  to  vary  from  25  to  30^  in  length,  with  a  breadth  of 
about  5^.  Waldeyer1  gives  the  size  of  adult  odontoblasts, 
but  does  not  compare  them  with  developing  cells — a  point  of 
importance  which  seems  to  have  been  overlooked. 

It  seems  reasonable  to  suppose  that  this  diversity  of  size 
would  account  for  the  increase  of  calibre  of  the  fibril  (and 
therefore  tubule)  as  it  approaches  the  pulp.  Paul  (loc.  cit. 
p.  134)  mentions  that  at  the  period  of  time  when  the  dentinal 
matrix  has  reached  a  depth  of  ^o  mm.,  the  odontoblasts 
are  very  long,  but  remain  about  7.7/1  in  width.  In  the  ox 
they  may  attain  the  length  of  50/4.  According  to  Kolliker, 
the  stratum  of  the  membrana  eboris,  in  an  adult  pulp,  measures 
from  41  n  to  83 /z  in  thickness;  the  odontoblasts  themselves 
being  25/i  long,  and  4/z  to  4.5^  broad. 

(7)  Relationships  to  surrounding  structures: — 

The  author,  in  a  paper  written  in  1889,  showed  that  these 
cells  are  not  packed  closely  together,  but  are  separated  by 
wide  visible  spaces,  which  in  certain  cases  are  filled  with  a 
"homogeneous  substance,  and  small,  round,  and  angular 
cells."  It  is  necessary  to  add  that  this  is  the  case  in  develop- 
mental pulps,  there  being  only  a  slight  amount  of  intercellular 
tissue  in  most  adult  specimens.  There  are  visible  also  in  many 
1  Strieker's  Histology,  Vol.  i,  1870,  p.  476. 


122  THE    DENTAL    TISSUES 

instances,  fine  delicate  spiral  fibrils  of  connective  tissue  stretch- 
ing into  the  dentine  between  the  odontoblasts,  in  addition  to 
the  already  mentioned  structures.  These  fibres  are  not  nerves, 
but  form  what  may  be  termed  the  "supporting  fibres''  of  the 
pulp.  Reference  to  this  point  will  again  be  made  later  on 
(page  130). 

The  long  axes  of  the  odontoblasts  are  approximately  in  the 
same  direction  as  that  of  the  tubules — a  fact  well  brought  out 
in  transverse  sections  of  pulp  cut  in  situ,  and  best  observed  in 
its  narrowest  part. 

In  some  sections,  the  cells  are  separated  some  distance  by 
a  gap,  in  which  a  capillary  loop  may  lie  quite  close  up  to  the 
dentine,  and  also  pulp  matrix — viz.,  delicate  intercommuni- 
cating fibres.  And  in  young  pulps,  in  which  dentine  matrix 
is  still  being  produced,  many  of  the  cells  have  attached  to 
their  distal  ends  lines  of  "transitional  tissue"  which  Paul 
calls  "collars."  An  odontoblast  "collar"  or  shoulder  is  thus 
often  seen,  and  was  described  by  the  earlier  investigators  as 
a  lateral  or  median  process  of  the  cell.  Mature  cells  do  not 
possess  it,  only  those  of  earlier  stages  of  growth  exhibiting  it.  A 
"collar"  nearly  always  adheres  to  the  dentine  matrix,  but  very 
often  to  the  cells  themselves;  is  more  highly  refractile  than 
any  other  part  of  the  cells,  and  is  the  only  portion  in  which 
they  are  in  mutual  contact.  It  is  important  to  notice,  how- 
ever, that  a  "collar"  is  not  part  and  parcel  of  the  odontoblast. 
It  is  pierced  by  its  dentinal  process.  It  is  probably  derived 
from  the  pulp  matrix,  and  really  consists  "of  a  delicate  net- 
work of  pulp  fibrils  woven  about  the  necks  of  the  odonto- 
blasts upon  which  the  secretion  of  the  latter  is  poured  and 
solidifies  to  form  the  dentine  matrix."  This  is  the  interpre- 
tation supplied  by  Paul;  but  while  the  author  agrees  with  the 
histological  appearances  just  described,  he  cannot  see  his  way 
clear  to  accept  Paul's  exposition  or  statement  as  to  the  lime- 
bearing  functions  of  the  odontoblasts. 

(5)  In  structure,  the  cytoplasm  of  the  odontoblasts  possesses 
a  coarse  degree  of  granularity,  which  does  not  disappear  on  the 
addition  of  a  weak  acid,  and  is  apparently  unaffected  by  glyc- 
erine, and  certain  other  chemical  re-agents.  The  distal  ends 


THE    DENTAL    PULP  123 

of  the  cells  when  young  are  apparently  clear  and  homogeneous, 
the  granularity  being  confined  to  the  lower  four-fifths.  In 
transverse  section,  this  granularity  is  due  to  either  (i)  a  coarse, 
deeply  staining  reticulum  or  spongioplasm,  (ii)  metaplastic 
inclusions,  or  to  (iii)  the  presence  of  numerous  translucent 
globules  (?  of  first-formed  calcoglobulin).  The  author  has 
failed  to  see  the  clear  zone  in  adult  odontoblasts,  and  considers 
that  the  spongioplasm  becomes  coarser  through  thickening  of 
the  nodes  of  the  spongioplasm  as  time  goes  on,  and  the  amount 


FIG.  99. — Section  of  tooth  germ  before  the  surface  cells  of  the  pulp  have 
undergone  any  differentiation.  Magnified  250  times.  (Photomicrograph  by 
Paul.) 

of  the  hyaloplasm  is  proportionately  diminished.  Hence  he 
again  differs  from  Professor  Paul  in  his  belief  that  the  clear 
zone  is  due  to  calcoglobulin. 

The  nucleus  of  an  odontoblast  is  large,  ellipsoidal,  and  promi- 
nent, and  is  situated  at  the  basal  extremity  of  the  cell.  Its 
wall  is  well-defined,  and  its  karyoplasm  pronounced.  Occa- 

1  In  this  connection  a  remark  by  Professor  Schafer  ("Quain's  Anatomy"  vol.  I., 
part  II.,  p.  174,  1898),  is  of  profound  significance:  "It  would  seem  that  the 
presence  of  certain  inorganic  substances,  and  especially  calcium,  is  essential  to 
the  life,  and  therefore  to  the  functions  of  protoplasm;  but  in  what  manner  the 
lime  may  be  combined  with  the  organic  basis  of  the  living  material,  remains  as 
yet  quite  undetermined." 


124 


THE   DENTAL    TISSUES 


FIG.  loo. — A  later  stage  than  Fig.  99.  Shows  surface  pulp  cells  becoming 
arranged  in  a  fairly  regular  layer,  with  their  chief  processes  directed  towards  the 
ameloblasts.  Magnified  250  times.  (Photomicrograph  by  Paul.) 


FIG.  101. — Shows  complete  evolution  of  surface  pulp  cells  They  have  pro- 
duced a  superficial  fibrous  layer,  and  their  nuclei  are  now  in  a  "resting"  state. 
The  odontoblasts  have  not  yet  appeared.  Magnified  250  times.  (Photomicro- 
graph by  Paul.) 


THE   DENTAL   PULP 


12: 


•  *- <iW>Wf '<- 




FIG.  102. — Shows  the  line  of  "transitional  tissue"  along  the  top  of  the  odonto- 
blasts.  At  one  place  it  stretches  across  a  gap  between  two  cells  caused  by  the 
intervention  of  a  blood-vessel  undergoing  degeneration  Magnified  250  times. 
(Photomicrograph  by  Paul.) 


FIG.  103. — A  very  thin  section  of  odontoblasts,  showing  the  pulp  fibres  in- 
vesting them,  and  ending  in  the  "transitional  tissue"  forming  the  shoulder  or 
collar  of  each  cell.  Magnified  340  times.  (Photomicrograph  by  Paul.) 


126  THE   DENTAL   TISSUES 

sionally  nucleoli  may  be  found.  The  nucleus  is  usually  placed 
at  the  centripetal  end  of  the  cell  as  has  been  already  stated;  but 
Paul  has  shown  that  it  may  be  found  in  the  middle,  and  occa- 
sionally quite  at  the  distal  end,  where  its  long  axis  lies  trans- 
versely to  the  cell.  In  this  latter  case,  however,  it  must 
not  be  forgotten  that  the  odontoblast  itself  is  very  short,  or 
has  been  cut  obliquely  so  as  to  appear  short.  If  a  cell  was 
lying  a  little  out  of  the  level  plane  of  its  neighbours,  in  a  ver- 
tical section,  the  nucleus  would  probably  appear  higher  in 
the  body  of  the  cell  than  usually  obtains.  Paul  thinks  that 
it  exhibits  an  exhausted  condition,  and  has  ceased  to  grow. 
An  odontoblast  may  have  two  nuclei  in  the  same  cell,  a  "con- 
dition by  no  means  uncommon,"  and,  rarely,  atrophied  nuclei 
have  been  observed  by  Paul  in  the  dentinal  fibril,  just  beyond 
the  transitional  tissue.  These  appearances  are  interpreted 
by  him  as  being  due  to  coalescence  of  two  odontoblasts, 
the  lower  cell  reinforcing  and  rehabilitating  the  degenerated 
upper  odontoblast. 

(e)  The  processes. — These  cells  are  remarkable  for  their  polar 
offshoots,  which  may  be  classified  as  (i)  central  or  basal;  and 
(ii)  peripheral  or  dentinal. 

Of  these,  the  first  named  are  most  easily  observed  in  sections 
when  ordinary  stains  are  used,  but  the  latter  cannot  be  so  clearly 
demonstrated  unless  special  methods  of  staining  with  haema- 
toxylene  or  gold  chloride  are  adopted.  Carmine  and  rubine  and 
a  few  aniline  dyes  show  them  also. 

(i)  The  peripheral  poles  of  the  odontoblasts,  extend  into 
and  enter  the  tubules  of  the  dentine,  and  are  here  called  dentinal 
fibrils.  In  some  cases  they  are  bifurcated:  several  fibrils  may 
emanate  from  one  cell;  and  nothing  else  can  be  seen  entering 
the  tubule.  Boll1  has  counted  as  many  as  six  processes  belong- 
ing to  one  cell. 

The  length  of  a  peripheral  process  of  an  odontoblast  may 
measure  4  or  5  mm.  It  thus  may  measure  in  extent  one 
hundred  and  fifty  times  the  length  of  the  cell  body.  This  fact 
alone  raises  an  odontoblast  to  a  much  higher  level  than  the  usual 
cells  of  a  mesodermic  tissue.  As  a  matter  of  fact,  the  dentinal 

1  "Untersuch.  der  Zahnpulpa."     Archil,,  fur  Mikrosk.  Anal.,  p.  73,  1868. 


THE    DENTAL   PULP  127 

fibril  issuing  from  an  odontoblast  renders  this  cell  one  of  the 
most  extraordinary  in  the  body.  In  the  human  economy 
no  more  remarkable  cellular  units  are  known  microscopically 
than  the  cell  bodies  of  certain  neurones,  which  may  possess,  as 
processes,  axones  extending  to  a  distance  varying  from  3ju  or 
4/u  to  one  metre  in  length.  Second  to  these  are  the  truly 
marvellous  odontoblasts  whose  processes — the  dentinal  fibrils — 
may  measure  4  mm.  There  can  be  no  doubt  whatever  that 
these  wonderful  cells  possess  high  functional  possibilities. 

(ii)  It  is  no  difficult  task  to  demonstrate  the  basal  offshoots  of 
the  odontoblasts.  They  are  exceedingly  thin  and  may  inter- 
communicate with  each  other.  This,  however,  is  not  at  all 
satisfactorily  proved.  They  present  no  varicosities  of  surface, 
are  not  swollen  or  twisted,  and  take  the  stain  less  deeply 
than  other  portions  of  the  pulp  tissue.  They  are  invisible  in 
young  developing  cells.  Special  stains,  such  as  Golgi's, 
Stroebe's,  or  methylene  blue  have  failed  up  to  the  present  time 
to  trace  back  these  central  poles  to  the  terminations  of  the 
nerves  of  the  pulp. 

According  to  Magitot,1  the  basal  processes  of  the  odonto- 
blasts are  continuous  with  the  branches  of  large  reticulate 
cells,  situated  as  a  layer,  beneath  them.  These  latter  cells  are 
placed  in  direct  line  with  the  nerve  terminations  (see  diagram, 
Fig.  127).  In  this  manner,  the  sensibility  of  the  dentinal  fibril 
might  be  accounted  for.  Recent  workers  have  not,  however, 
corroborated  Magitot's  views,  and  his  deductions,  in  the  light  of 
more  modern  research,  would  seem  to  be  incorrect. 

In  the  dental  pulp  of  the  ox,  these  basal  processes  assume  a 
large  size.  If  an  incisor  is  removed  from  the  jaw  of  an  ox, 
immediately  after  the  animal  has  been  slaughtered,  and  then 
broken  longitudinally  in  a  vise,  the  basal  poles  may  be  demon- 
strated in  a  few  minutes,  while  still  fresh.  A  small  piece  of  the 
membrana  eboris  is  removed  and  teased  in  salt  solution;  while 
carmine  or  chloride  of  gold  clearly  stains  the  long  processes. 

Aitchison  Robertson2  has  studied  these  offshoots  in  the  ox,  and 

1  Journal  de  I' Anatomic  de  M.  Charles  Robin,  Paris,  1881. 

2  "On  the  Relation  of  Nerves  to  Odontoblasts,  and  on  the  Growth  of  Dentine." 
Trans.  Roy.  Soc.  of  Edinburgh,  p.  323,  1891. 


128 

he  reports  that  "  odontoblasts  were  seen  which  had  become 
separated  from  the  other  cells,  and  had  drawn  out  along  with 
them  their  internal  or  root  process.  This  was  in  some  cases  of 
great  length,  and  could  be  traced  for  some  distance  into  the 
pulp.  In  other  cases,  part  of  the  dentinal  fibril  still  remained 
attached  to  one  extremity  of  the  separated  odontoblasts,  while 


FIG  104. — Portion  of  surface  of  the  pulp  teased  in  potassium  anhydrochro- 
mate  solution.  Shows  the  very  long  central  process  belonging  to  each  odonto- 
olast  and  entering  the  substance  of  the  pulp.  The  odontoblast  has  fallen  off 
in  many  cases,  and  leaves  the  central  process  projecting  like  a  fine  hair  or  nerve 
fibre.  (After  Aitchison  Robertson.) 


FIG.   105. — Apparent   direct   continuation   of  the  root   process   of   the   odonto 
blasts  with  the  axone  of  a  nerve.      (After  Aitchison  Robertson.) 

from  the  other  extremity,  the  long  internal  root  process  was 
seen  extending  into  the  pulp."  The  processes  sometimes 
measured  even  twelve  times  the  length  of  the  odontoblast  cell, 
and  in  some  instances  passed  into  groups  of  nerve  fibres,  amongst 
which  they  apparently  ran  for  some  distance  before  they  ac- 
quired a  myelinic  sheath.  This  author  significantly  ob- 
serves: "I  am  convinced  that  the  central  processes  of  the 

odontoblasts  become  continuous  with  the  nerve  fibrils 

The  long  central  process  seems  to  become  the  axis-cylinder  of  a 


THE    DENTAL   PULP  129 

nerve  fibre,  which  gradually  acquires  a  primitive  sheath  in  which 
the  medullary  or  white  substance  slowly  accumulates,  till  an 
ordinary  medullated  nerve  results.  ...  It  is  very  difficult 
to  say  whether  all  the  odontoblasts  send  in  their  long  processes 
to  join  the  nerve  fibres." 

It  is  a  histological  fact  that  odontoblasts  possess  processes 
running  towards  the  pulp;  but  it  has  not  been  proved,  in  spite 
of  Robertson's  work,  that  they  are  the  direct  continuation 
of  the  pulp  myelinic  nerve-fibres. 

Their  existence  is  doubted  by  Hertz  ("  Untersuch.  iiber 
den  feineren  Bau  und  die  Entwickelung  der  Zahne,"  in  Vir- 
chow's  "Archives,"  Bd.,  37,  1866)  and  by  Paul. 

(f)  There  is  a  certain  amount  of  analogy  existing  between 
the  odontoblasts,  and  certain  epitheloid  cells,  found  in  the 
olfactory  regions  of  man  and  animals,  in  the  ganglionic  layer 
of  the  retina,  and  the  auditory  cells  of  the  macula  lutea  of  the 
membranous  labyrinth.  Their  processes  are  somewhat  similar, 
their  structure  identical,  their  shape  modified  only  by  the 
mutual  apposition  of  neighbouring  cells. 

(2)  The  Other  Pulp  Cells 

The  cells  of  the  pulp  proper,  viz.,  those  situated  in  the 
central  portions  of  the  tissue,  differ  in  size  and  shape  during 
the  various  stages  of  the  growth  of  that  organ.  In  developing 
teeth  they  are  large,  and  have  rounded  angular  or  spindle- 
shaped  outlines.  In  short,  they  partake  of  the  nature  of  em- 
bryonic cells  generally.  Their  nuclei  are  large,  prominent, 
oval  or  lenticular,  contain  karyosomes  and  chromatin,  and  are 
devoid  of  nucleoli.  Near  the  superficial  portions  of  the  pulp 
they  are  very  loosely  held  in  the  reticulum  by  the  connective 
tissue  stroma;  and  here,  more  spindle  cells  are  visible. 

In  adult  teeth,  the  pulp  cells  are  chiefly  stellate  or  angular 
in  shape,  with  numerous  branches.  Their  number  is  greater, 
as  a  rule,  than  the  ordinary  round  cells;  but  cells  of  any  de- 
scription are  comparatively  few.  The  branches  are  long  and 
multiplied,  and  interlace  with  one  another,  giving  the  pulp 
somewhat  the  appearance  of  a  mucoid  tissue.  Fewer  cells 
exist  in  the  radicular  region  of  the  organ.  A  few  insignificant- 

9j 


130  THE    DENTAL    TISSUES 

looking  odontoblasts  are  found;  but  the  mass  of  the  pulp  seems 
composed  of  bundles  of  thick  and  thin  connective  tissue  fibres 
and  cells  running  in  all  directions. 

The  morphology  of  the  individual  cells  is  best  studied  in 
fresh  pulps  which  have  been  teased-out  in  physiological  salt 
solution,  and  suitably  stained. 

B 

The  Connective  Tissue  Stroma 

Extending  throughout  the  pulp  in  every  direction,  like  an 
exceedingly  minute  net,  is  the  connective  tissue  stroma  or 
scaffolding  in  which  the  cells  are  imbedded.  This  framework 
serves  two  purposes,  as  an  imbedding  material  for  the  pulp 
cells,  and  as  a  support  to  sling  up  the  soft  delicate  organ  in  its 
bony  casing,  in  much  the  same  way  as  marrow  is  supported 
in  the  medullary  cavities  of  bone.  The  fine  fibres  appear  some- 
times to  enter  the  dentinal  tubules,  but  they  are  most  often 
seen  attached  to  the  free  margin  of  the  matrix  of  the  dentine, 
where,  most  likely,  they  are  in  reality  the  odontogenic  fibres. 
The  author  in  1893  was  the  first  to  draw  attention  to  those 
"  supporting  fibres  "  of  the  pulp.  They  are  generally  recognised 
by  their  spiral  appearance,  and  have  recently  again  been 
studied  by  Von  Korff  (Archiv.  fur  Micros.  Anat.,  1907)  and 
Studnicka  (Anat.  Anzeiger,  1907).  It  is  probable  that  these 
connective  tissue  fibres  are  considered  by  Howard  Mummery 
(Proc.  Roy.  Soc.  Medicine,  1912)  to  be  the  terminations  of  the 
myelinic  nerve  fibres  of  the  pulp. 

In  the  sub-odontoblast  region  of  the  pulps  of  adult  teeth  the 
basal  layer  of  Weil  is  seen.  This,  first  described  by  the  late 
W.  A.  Weil,  of  Munich,1  in  his  monograph  on  the  Dental  Pulp, 
consists  of  a  distinct  clear  layer  of  fibres  with  a  great  scarcity 
or  even  absence  of  cells.  In  describing  it,  he  wrote:  "The 
layer  contains  no  cellular  elements  or  nuclei;  it  appears  rather 
as  a  web  of  extremely  fine  fibrils,  which  do  not  run  perpen- 
dicularly through  the  layer,  but  running  obliquely  towards  the 
deeper  layers,  interlace  with  one  another  in  a  crosswise  direc- 
1  "Zur  Histologie  der  Zahnpulpa."  Leipzig,  p.  55,  1887. 


THE    DENTAL    PULP 


&pvV|J'/ 

fr^™^  »t  T,  ^^Wi*    \  ••*'"      .  VL      ;    rt  i 


ifv     wl  r'T-  ^    t  PU1P'     PrePared  b^  the  Author's  process,  and  stained 

with     Ehrhch  s     acid    ha3matoxylene.      Magnified    750    times.     A.   Artery     c 
capillary;  v.  Vein;  p.  Pulp  tissue  proper;  F.  Fasciculus  of  myelinic  nerve  fibres 


:i'3*2: :    :  :;.     •  THE  DENTAL  TISSUES 

tion.  ...  It  may  be  said,  with  perfect  security,  that  they 
arise  from  the  projecting  basal  ends  of  the  odontoblasts.  It  is, 
however,  surprising  that  these  offshoots  do  not  follow  the  axial 
directions  of  the  odontoblasts,  but  turn  sideways  to  one  direc- 
tion or  another,  and  thus  form  the  crossings." 

The  basal  layer  measures  at  the  coronal  part  of  the  pulp 
0.025  mm.  in  diameter,  and  gradually  becomes  diminished  in 
size,  until  it  no  longer  exists  in  the  radicular  region. 

This  statement  is  corroborated  by  Partsch,1  of  Breslau, 
and  deserves  great  attention. 

Further,  Howard  Mummery2  refers  largely  to  this  in  a 
recent  paper,  where  he  says: — "According  to  my  experience 
the  layer  is  not  visible  in  young  teeth  in  the  situation  of  the 
rapidly  depositing  dentine  at  the  open,  uncompleted  end  of 
the  root."  And  it  may  be  added,  that  the  author  has  repeatedly 
observed  it  in  the  mature  pulps  of  deciduous  and  permanent 
teeth  as  well  as  in  certain  pathological  conditions;  but  never  in 
young  growing  teeth.  Professor  Paul  has,  however,  noticed 
"a  clear  zone  of  tissue  just  beneath  the  most  actively  growing 
young  odontoblasts."  He  declares: — "It  seems  to  me,  after 
many  careful  examinations,  that  the  appearance  is  not  due  to 
the  presence  of  a  specialised  tissue,  but  is  simply  owing  to  a 
rarefaction  of  the  pulp  preceding  the  active  extension  of  the 
odontoblasts,  which  are  of  course  progressing  inwards  through 
the  pulp  matrix." 

Regarding  the  exact  nature  of  the  basal  layer,  it  is  a  difficult 
matter  to  decide.  It  is  certainly  fibrous;  but  whence  the  fibres 
come  and  go,  and  whether  the  whole  layer  is  an  artificial  product 
or  not  is  as  yet  undecided. 

Weil  himself  considered  that  the  fibres  were  undoubtedly 
continuous  with  the  odontoblasts,  and  might  thus  be  a  means 
of  communication  between  them  and  the  nervous  system  of 
the  pulp.  He  never  was  able  to  prove,  however,  that  these 
delicate  fibres  were  amyelinic  nerves.  Repeated  attempts 
at  differential  staining  to  ascertain  if  they  were  of  a  nervous 
character  have  failed.  A  stray  capillary  may  cross  the  layer 

1  Deutsche  Monatsschrift  fiir  Zahnheilkunde,  p.  322,  1892. 
2  Journal  of  British  Denial  Association,  p.  779,  1892. 


THE    DENTAL    PULP 


133 


and  get  into  the  spaces  between  the  odontoblasts.  Howard 
Mummery  does  not  believe  that  all  the  fine  fibres  are  in  con- 
tinuity with  the  odontoblasts;  many  of  them  penetrate  through 
the  layer  and  enter  the  dentine  matrix. 

Its  existence  as  a  true  histological  structure  is  doubted  by 
Ebner  and  Rose. 

von  Ebner  says: — "The  odontoblasts  are  attached  to  the 
dentine  by  means  of  the  dentinal  fibrils — they  cannot,  there- 
fore, when  the  inner  portions  of  the  pulp  shrink  up  (through 


DZ 


FIG.  107. — The  pulp  in  situ.  Prepared  by  the  Author's  process,  and  stained 
with  Ehrlich's  acid  hsematoxylene.  Magnified  250  times.  B.  The  basal  layer 
of  Weil;  o.  Odontoblasts;  D.Z.  Dentogenetic  zone. 

the  action  of  reagents  used  in  the  Koch-Weil  balsam  process) 
be  very  well  torn  awray;  but  the  layer  immediately  under  the 
odontoblasts  will  seek  to  approach  the  centre  of  the  pulp,  and 
before  it  comes  to  a  rupture,  the  tissue  elements  which  form 
the  connection  of  the  odontoblast  layer  with  the  pulp  lying 
beneath,  will  be  very  strongly  stretched.  These  tissue  elements 
are  chiefly  fibres,  and  in  this  way  a  layer  of  fibres  can  be  arti- 
ficially produced  which  before  was  non-existent 

Dr.  Weil  shows  that  from  the  tissue  of  the  pulp,  rich  in  cells, 
which  is  found  beneath  the  membrana  eboris,  numerous  fibres 


134  THE    DENTAL   TISSUES 

penetrate  toward  the  odontoblasts.  But  that  these  fibres, 
in  life,  exist  as  a  special  basal  layer  cannot  be  proved  by  Dr. 
Weil's  method." 

And  thus  also  Rose. 

But  Howard  Mummery  considers  that  the  facts  of  the  non- 
distortion  of  blood-vessels  in  the  layer,  as  also  its  absolute 
disappearance  at  the  growing  extremity  of  the  roots  of  teeth 
with  large  apical  foramina  must  be  taken  into  account,  and 
disprove  the  theory  of  shrinkage  of  the  pulp. 


The  Vascular  Supply 

The  pulp  is  freely  vascularized  by  branches  which  are 
derived  from  the  Posterior  Dental,  Infra-orbital  and  Mandib- 
ular  divisions  of  the  Int.  maxillary  artery. 

They  enter  the  teeth  through  the  apical  foramina  of  their 
roots,  generally  as  one  large  trunk,  or  as  three  or  more  small 
ones.  Shortly  after  their  entrance  into  the  pulp,  the  vessels 
branch  repeatedly,  become  smaller  in  calibre,  until  near  the 
surface  they  form  a  simple  capillary  network  which  may 
measure  8ju  to  i2;u  in  width.  It  may  be  stated  in  general 
terms  that  there  is  no  collateral  circulation  in  the  pulp.  In 
this  respect  the  condition  resembles  that  which  obtains  in 
the  terminal  blood-vessels  of  the  brain,  the  arteria  centralis 
retina  of  the  eye,  and  in  a  lesser  degree  also  in  the  walls  of  the 
heart. 

During  the  period  of  development  the  vascular  system 
covers  a  large  area  of  the  dentine  papilla.  The  main  arterial 
trunk,  proceeding  in  a  longitudinal  direction  through  the 
centre  of  the  tissue,  decreases  in  diameter  very  gradually, 
till  near  the  edge  of  the  dento-genetic  zone,  when  it  almost 
suddenly  and  rapidly  becomes  narrower,  and  is  ultimately 
lost  in  a  dense  capillary  plexus.  The  branches  have  the 
peculiarity  that  very  often  they  issue  at  or  about  right  angles 
with  the  main  vessel  (see  Plate  I). 

In  adult  pulps,  this  angular  method  of  division  is  not  so 


THE    DENTAL    PULP 


135 


evident;   the   larger   vessels   are  located   chiefly  in   the  axial 
portion,  whence  numerous  branches  pass  in  all  directions. 

In  the  cornual  regions  many  anastomatic  capillary  loops 
have  their  convexities  directed  towards  the  dentine.  As  a 
rule,  these  capillaries  extend  as  far  as  the  basal  layer  of  Weil; 
but  occasionally,  as  has  been  already  mentioned,  one  or  more 
may  cross,  and  pass  between  the  odontoblasts  (Fig.  92). 


EC 


FIG.  108. — A  sympathetic  nerve  fibre  running  along  the  wall  of  a  capillary  of  the 
dental  pulp.  Highly  magnified.  N.F.  Nerve  fibre;  E.G.  Endothelial  cell  of  cap- 
illary wall;  N.  Nucleus  of  pulp  cell.  Preparation  and  photomicrograph  by  Dr. 
H.  Box,  Royal  College  of  Dental  Surgeons,  Toronto. 

The  arteries  vary  in  size,  in  different  pulps,  but  a  main  trunk 
may  measure  about  83  ju  in  width,  while  the  diameter  of  the 
lumina  of  the  capillaries  is  roughly  about  S/j,. 

The  former  are  accompanied,  not  only  by  their  respective 
veins,  but  also  by  fasciculi  of  myelinic  nerves,  which  run 
side  by  side,  sometimes  so  closely  that  nothing  but  a  few 
connective  tissue  fibres  and  cells  intervene  between  the  outer- 
most portion  of  the  external  coat,  or  tunica  a-dventitia,  of  the 
artery,  and  the  perineurium  of  the  latter. 

By  selective  staining  it  is  possible  to  demonstrate  the  sym- 
pathetic nerve  fibres  which  are  distributed  to  the  middle  and 
outer  coats  of  the  vessels. 


136  THE    DENTAL    TISSUES 

Properly  stained  horizontal  sections  of  pulps  reveal  in  a 
most  beautiful  manner  both  the  approximate  number  of 
blood-vessels  and  also  their  differences  in  structure.  In 
typical  canine  pulps,  cut  crosswise  through  the  cervical  region, 
the  author  has  counted  10  of  the  former.  The  typical  veins, 
several  of  which  were  just  macroscopically  visible,  exceeded 
this  number  by  14,  while  the  capillaries  were  practically  count- 
less.1 

Histologically  considered,  the  vessels  of  the  pulp  differ 
very  considerably. 

The  Arterioles. — Structure. — The  wall  of  each  small  artery 
consists  of  three  coats,  viz.,  the  tunica  intima,  media  and 
adventitia,  the  first-named  being  indistinguishable,  except 
under  high  magnifications,  and  the  media  being  very  marked. 

(i)  Tunica  intima. — Here  is  found,  forming  the  lining  of 
the  lumen  of  the  vessel,  a  flattened  layer  of  thin,  singularly 
elliptical  endothelial  cells,  each  having  a  round  or  oval  nucleus. 
When  the  blood  corpuscles  have  not  been  retained  in  situ 
in  the  section,  the  cells  may  be  sometimes  seen  to  project 
into  the  lumina.  External  to  the  endothelial  lining  is  an 
attenuated  double  wavy  line,  continuously  circling  the  artery. 
This  is  known  as  the  elastic  layer  of  the  inner  coat,  and  it  is 
made  up  of  numerous  longitudinal,  closely  arranged  yellow 
elastic  fibres,  (ii)  The  Tunica  media  is  composed  mainly 
of  plain  muscular  tissue,  which  makes  this  coat  the  thickest 
and  most  prominent  of  all.  It  is  arranged  circularly  round  the 
vessel,  and  its  component  parts  are  made  up  of  unstriated 
muscle  fibres  with  elongated  nuclei.  The  elastic  tissue  of  the 
larger  arteries  is  wanting  in  this  coat  in  the  vessels  of  the  pulp, 
(iii)  The  Tunica  adventitia,  consisting  of  areolar  or  connective 
tissue  fibres  and  cells,  with  nuclei  placed  in  the  long  axes  of  the 
cells,  represents  the  outer  coat  of  the  artery.  These  fibres 
and  cells,  too,  run  circularly  round  the  vessels  and  blend  inti- 
mately with  the  connective  tissue  fibres  of  the  pulp. 

1  These  figures  are  introduced  in  this  connection,  in  order  to  supply  the  reader 
with  some  idea  as  to  the  numbers  that  may  be  computed,  i.e.,  to  demonstrate 
that  the  arteries  of  the  pulp  are  not  counted  in  hundreds,  but  in  tens.  It  is 
obvious  that  the  numbers  given  are  never  constant. 


THE    DENTAL    PULP  137 

Nerd  vasorum  are  present  in  this  coat.  They  belong  to  the 
sympathetic  nervous  system. 

The  Veins  differ  from  the  arteries  in  the  fact  that  the  size  of 
the  middle  coat  is  greatly  reduced,  and  the  endothelial  cells  are 
shorter  and  broader.  Otherwise  they  resemble  the  arteries. 
In  sections,  they  are  easily  differentiated  from  the  other  blood- 
vessels in  having  a  very  much  greater  diameter.  They  are 
non-collapsible  in  the  pulp,  have  no  valves,  and  retain  the 
rounded  outlines  of  their  walls.  This  is  doubtless  due  to  their 
strong  support  by  means  of  the  stroma  which  permeates  the 
pulp  tissue. 

The  walls  of  the  Capillaries  are  exceedingly  delicate,  being 
formed  by  a  single  layer  of  endothelium,  which  is  a  continuation 
of  the  endothelial  lining  of  the  arteries,  on  the  one  side,  and  the 
veins  on  the  other.  The  smallest  capillary  walls  may  consist  of 
only  two  or  three  of  such  cells,  which,  in  this  case,  are  curved  to 
form  the  interior  of  the  tube.  The  nuclei  are  marked  and  the 
karyoplasm  pronounced  (see  Fig.  106). 

There  are  no  traces  of  any  organized  lymphatic  system  in  the 
dental  pulp.  That  is  to  say,  evidences  of  the  existence  of 
endothelially-lined  lymphatic  capillaries  or  vessels  are  wanting. 
Pericellular  and  intercellular  lymph  spaces  or  tissue  spaces  are 
everywhere  apparent,  as  also  are  those  around  the  blood-vessels 
and  nerve  bundles.  The  pulp  is  saturated  with  lymph  which  is 
derived  from  the  blood  plasma,  as  an  exudation  from  the  capil- 
laries. It  permeates  the  pulp  tissue  and  exudes  into  the  den- 
tinal  ^tubules  around  the  odontoblast  processes.  It,  however, 
does  not  pass  into  lymphatic  vessels,  and  does  not  leave  the  pulp 
by  any  such  channels.  Yet  Schweitzer,  in  an  elaborate  article 
(Arch.  f.  mikr.  Anal.,  1907)  claims  that,  by  careful  injection,  he 
has  succeeded  in  demonstrating  tufts  of  lymphatic  capillaries 
in  the  coronal  portion  of  the  pulp,  which  collecting  the  lymph  of 
that  neighbourhood,  conveys  their  contents  into  one  or  two  wide 
lymphatic  vessels  which  issue  from  the  apical  foramina  of  the 
teeth  in  company  with  the  blood-vessels.  The  dental  pulp  is 
one  of  those  few  parts  of  the  body  which  is  devoid  of  any  lym- 
phatic system. 


138  THE    DENTAL   TISSUES 

D 

The  Nervous  System 

As  eliciting  the  closest  attention  on  the  part  of  many  thinkers 
and  writers,  as  presenting  a  truly  fascinating  and  profoundly 
interesting  field  of  speculation,  as  affording  ample  opportunities 
for  most  brilliant  work  in  original  research,  the  study  of  the 
nervous  sytem  of  the  dental  pulp  may  claim  to  be,  of  all  dental 
histological  subjects,  of  the  first  importance,  instruction,  and 


FIG.   109. — The  plexus  of  Raschkow,  teased  out,  and  stained  with  chloride  of 
gold.      Magnified  250  times. 

value.  One  is  completely  astonished  at  the  mass  of  literature, 
old  and  new,  which  has  been  devoted  to  it.  Its  bibliography  is 
manifold,  and  in  itself  would  furnish,  if  gathered  in  one  volume, 
most  illuminating  reading.  Yet  in  spite  of  the  earnest  labours 
of  one  half-a-century,  it  is  amazing  to  recall  the  fact  that  while 
so  much  is  known  about  it,  so  much  is  still  unknown — the  actual 
methods  of  the  peripheral  distribution  of  the  myelinic  (medul- 
lated)  nerves  being  buried  in  obscurity.  True,  that  some 
of  the  earlier  histologists  solved  most  carefully  in  suo  modo 
this  particular  and  difficult  problem;  true,  that  modern 


THE   DENTAL   PULP 


139 


methods  of  preparing  the  hard  and  soft  tissues  for  micro- 
scopical examination  have  shed  new  light  on  it;  it  still  remains 
to  be  noted  that  the  ana.tom.ical  data  and  physiological 
principles  involved  in  the  phenomena  which  give  rise  to  pain 
in  the  teeth — the  whole  innervation  of  the  pulp — the  direct 


CTC 


Raw     , 

•  J 

usar 


FIG.    no.  —  Similar  to  Fig.  106. 
Prepared  by  the  Author's  process. 
C.T.C.   Connective  tissue   fibres   and  cells; 
bundles. 


To  show  six  nerve  bundles  cut  transversely. 
Stained  with  rubine.      Magnified  750  times. 
c.   Capillary;     M.   One  of    the    nerve 


course  by  which  sensation  is  conducted  from  the  dentine  or 
enamel  to  the  cortical  areas  of  the  cerebral  hemispheres  cannot 
be  considered  satisfactorily  determined.  But  its  capability  of 
solution  is  unquestionable. 

Here  an  attempt  will  be  made  to  describe  the  chief  recognised 
facts,  and  some  arguments  in  this  nebulous  matter.  The  nerv- 
ous system  of  the  dental  pulp  consists  of  the  peripheral  pro- 


140  THE    DENTAL   TISSUES 

longations  and  terminations  of  certain  cerebro-spinal  ganglionic 
neurones  emanating  from  the  upper  and  lower  sensory  nuclei  in 
the  medulla  and  fourth  ventricle,  and  passing  through  to  the 
Gasserian  ganglion.  They  are  cellulipetal,  and  while  con- 
stituting the  peripheral  axones  of  receptive  afferent  neurones, 
they  are  essentially  the  distal  telodendria  of  the  peripheral  sen- 
sory neurones.  They  terminate  structurally  like  the  teloden- 
dria of  the  other  ordinary  sensory  nerves,  and  probably  arborize 
about  the  odontoblasts  on  the  surface  of  the  pulp  and  do  not 
penetrate  the  dentinal  tubules.  The  blood-vessels  of  the  pulp 
are  under  the  trophic  control  of  fibres  of  the  sympathetic 
system.  It  will  be  convenient  to  consider  the  subject  under  the 
following  headings:  The  myelinic  nerves,  their  (i)  method  of 
distribution,  (ii)  structure,  and  (iii)  terminations  in  (a)  fishes, 
(6)  reptiles,  (c)  mammals. 

(i)  Method  of  Distribution. — Emerging  from  the  "indifferent 
tissue"  of  the  periodontal  membrane,  in  company  with  the  main 
arterial  trunks,  and  entering  the  apical  foramina  of  the  teeth,  the 
bundles  of  myelinic  and  sympathetic  nerve  fibres  pass  collec- 
tively into  the  pulp,  in  lines  directly  corresponding  to  its  long 
axis.  There  are  thus  several  funiculi  colligated  into  sheaves; 
and  without  undergoing  much  appreciable  diminution  in  num- 
bers, they  extend  into  the  soft  tissue,  and  maintain  a  more  or 
less  parallel  direction  with  the  outlines  of  the  dentinal  walls. 
The  nervous  trunks  pass,  like  long,  straight  or  very  slightly 
wavy  lines,  in  this  way,  for  some  considerable  distance,  and 
then  begin  gradually,  as  they  approach  the  parieties  of  the  pulp, 
to  break  up  into  smaller  fasciculi;  until,  when  close  to  the  basal 
layer  of  Weil,  the  original  bundles  are  represented  only  by  two 
or  more  nerve  fibres  running  side  by  side.  In  many  instances, 
the  bundles  stretch  up  to  the  sub-odontoblast  region,  and  then, 
according  to  Rose  and  Gysi  ("  Portfolio  of  Microphotographs  of 
Dental  Histology,"  1895)  very  suddenly  burst  forth  in  myriads 
of  minute  scopiform  strands.  The  result  is  the  formation  of  an 
interlacing  of  fibres — the  plexus  of  Raschkow  (see  Fig.  109). 

In  every  case  the  chief  nerve  fasciculi  run  alongside  the  larger 
blood-vessels,  and  in  their  areas  of  distribution  follow  them 
closely,  and,  in  the  case  of  the  sympathetic  fibres,  penetrate 
their  external  coats. 


THE    DENTAL    PULP 


141 


FIG.   III. — Myelinic  nerve  fibres,  teased  out.     Stained  with  osmic  acid. ^Magni- 
fied 850  times.     R.  A  node  of  Ranvier. 


FIG.   112. — Similar  to  the  preceding.      Magnified  800  times. 


142  THE    DENTAL    TISSUES 

Towards  their  distal  arborisations  they  become  in  places  lobu- 
lated  or  varicose,  a  condition  which,  according  to  Schafer,1  is 
occasioned  by  pressure  or  traction  on  them,  causing  the  soft 
matter  "to  accumulate  at  certain  points,  whilst  it  is  drawn  out 
and  attenuated  at  others."  In  addition  to  these  occasional 
dilatations,  and  near  their  peripheral  distribution  they  divide 
into  branches — each  component  part  participating  in  the  divi- 
sion. By  oft-repeated  sub-division  the  fibres  become  much 
smaller. 

(ii)  In  structure,  the  myelinic  or  white  nerve  fibres  correspond 
with  those  found  elsewhere  in  the  cerebro-spinal  system  of  man, 
except  in  one  particular,  and  that  is  with  regard  to  size.  The 
individual  fibres  in  the  pulp  vary  from  1.5^  to  3/i  in  diameter. 
Kolliker  has  measured  them.  His  figures  are:  In  diameter, 
the  large  trunks  in  the  radicular  part  of  the  pulp,  are  62  fj.  to  8^; 
their  constituent  elements  3/i  to  6/x;  and  their  primitive  fibres 

2.5M  tO  34/z. 

Each  consists  of  (a)  the  axis-cylinder  of  Purkinje;  (j3)  the 
medullated  sheath  of  Schwann;  and  (7)  the  primitive  sheath 
or  neurilemma. 

(a)  The  axial  fibre,  or  axis-cylinder  process,  or  more  shortly 
the  axone,  extends  without  interruption  through  the  whole 
length  of  the  nerve  fibre,  from  its  origin  in  the  cell  body  in  the 
cerebrum  to  its  ultimate  ramifications  near  the  membrana 
eboris.  It  is  to-day  an  almost  certain  fact  that  the  axone  is 
always  a  direct  prolongation  of  a  branch  of  a  nerve  cell,  ex- 
tending far  away  from  its  origin,  but  yet  in  perfect  conti- 
nuity with  it.  Max  Schultze  in  i8372  observed  that  the  axone 
consists  not  of  a  single  cord  or  thread,  but  is  a  complex  structure 
made  up  of  many  fibrils  ("primitive  fibrillae")  imbedded  in 
fine  granular  material.  Obersteiner  told  Gowers3  that  he  had 
counted  as  many  as  fifty  such  primitive  fibrils  in  a  single 
axone,  each  fibril  having  a  separate  and  distinct  path  of 
conduction. 

1  "Quain's  Anatomy,"  Vol.  II.,  part  I.,  1912. 

2  Vide  Strieker's  "Histology." 

3  "The  neurone  and  its  relation  to  disease."  British  Med.  Journal,  Nov.  6th, 
1897. 


THE    DENTAL    PULP  143 

(j3)  The  myelin  sheath,  or  white  substance  of  Schwann,  is 
easily  identified  in  sections  of  the  pulp  when  stained  with  osmic 
acid,  the  action  of  which  is  to  render  the  fatty  matter  (which 
contains  lecithin)  of  the  myelin  a  dark  grey  or  black  colour. 

The  medulla  is  continuous,  but  presents  here  and  there 
breaks  in  its  continuity.  These  constrictions  are  known  as 
the  nodes  of  Ranvier.  Occurring  at  nearly  equal  intervals, 
they  divide  the  fibre  into  internodes.  The  white  substance 
has  undergone  a  certain  amount  of  shrinkage  at  a  node,  and 
is  quite  transparent,  but  in  addition  there  is  present  a  finely 
granular  stroma  rendered  evident  through  refraction  by  the 
fatty  matters  which  are  usually  found  in  it  (Fig.  in). 

The  nodes  of  Ranvier,  when  treated  with  various  stains, 
exhibit  other  markings.  In  this  way,  a  weak  solution  of  silver 
nitrate  reveals  the  crosses  of  Ranvier — in  which  the  cement 
joining  two  internodes,  and  a  small  portion  of  the  axone  are 
affected,  and  also  sometimes  Fromman's  lines — a  cross-stria- 
tion  of  the  axone  at  the  node;  and  a  i  per  cent,  solution  of 
osmic  acid,  minute  nodes  on  the  primitive  fibrils  of  the  axone 
with  the  black  constricting  ring  of  Ranvier  placed  outside 
(van  Gedoelst). 

Further  sub-divisions  in  the  medullary  sheath  are  found  in 
the  form  of  oblique  slits  passing  outwards  from  the  axone  to 
the  neurilemma.  These  are  called  "incisures,"  and  are  ren- 
dered apparent  by  the  use  of  osmic  acid  and  picro-carmine. 
They  split  up  the  internodal  myelin  into  a  series  of  short 
lengths  or  "cylinder  cones,"  the  bevelled  end  of  one  cone 
fitting  accurately  into  the  opposite  similar  end  of  the  neigh- 
bouring cone. 

In  addition  to  these  various  histological  structures  in  the 
myelinic  sheath  of  nerves,  there  exist  also,  when  suitably  stained, 
radial  virgate  striations,  as  well  as  a  more-or-less-coarse 
reticulum. 

(7)  The  primitive  sheath  or  neurilemma  forms  the  external 
covering  of  white  nerve  fibres.  It  is  an  exceedingly  delicate 
homogeneous  membrane  which  passes  over  every  node  of 
Ranvier,  and  possesses  in  the  mid-distance  of  an  internode  a 
large  flat  nucleus.  At  a  node,  the  neurilemma  is  probably 


144  THE   DENTAL   TISSUES 

discontinuous  with  the  axone,  because  of  the  intervention  of  the 
annular  constricting  band  of  Ranvier. 

A  horizontal  section  of  the  pulp  stained  carefully  with 
osmic  acid  or  haematoxylene  or  other  stains  displays  the 
nerve  bundles  cut  across.  Collectively  examined  they  show 
the  endoneurium — fine  connective  tissue  septa  passing  in 
between  the  individual  nerve  fibres,  as  processes  of  the  peri- 
neurium  which  surrounds  the  fascicule  itself.  Several  fas- 
ciculi are  invested  by  the  epineurium.  These  coverings — endo- 
neurium, perineurium,  and  epineurium — are  continued  to  the 
ultimate  terminations.  In  the  finest  branches  they  are  re- 
duced to  a  mere  connective  tissue  sheath,  the  sheath  of  Henle. 

The  sympathetic  nerve  fibres — fibres  of  Remak — are  the 
axones  of  neurones  belonging  to  the  sympathetic  system,  being 
distributed  to  the  blood-vessels  as  vaso-dilators  or  vaso-constric- 
tors.  They  are  amyelinic,  measure  i/z  to  2p  in  diameter, 
consist  of  axone  and  neurilemma,  and  terminate  as  telodendria 
composed  of  naked  axones. 

(iv)  Peripheral  Terminations  of  the  Nerves 

In  order  to  pave  the  way  to  some  knowledge  of  the 
anatomical  distribution  of  the  free  extremities  of  the  nerve 
fibres  in  the  dental  pulps  of  man,  it  will  be  expedient  and 
instructive  to  note  how  the  nerves  end  in  the  pulps  of  the 
teeth  of  fishes,  reptiles,  etc. 

(a)  In  Pisces 

Here  the  evidences  as  to  the  exact  mode  of  the  terminal 
arborization  of  the  sensory  nerve  fibres  are  quite  clear,  thanks 
to  the  splendid  labours  of  Gustav  Retzius.1  By  Golgi's  method 
of  staining,  he  succeeded  in  positively  demonstrating  in  the 
teeth  of  Gobius  and  Gasterosteus,  anatomical  conditions  which 
agree  in  all  essential  points.  Definite  types  of  nerve-branching 
were  observed. 

1  "Biologische  Untersuchungen,"  Xeue  Folge,  iv.,  v.  and  vi.,  1892,  1893,  and 
1894- 


THE  DENTAL  PULP 


145 


The  amyelinic  nerve  fibres  arising  from  a  dense  plexus  in 
the  soft  tissues  in  which  the  teeth  are  situated,  pass  into  the 
pulp  and  spread  out  thickly  to  form  free  endings  in  that 
tissue,  extending  upwards  towards  the  coronal  region,  and 
abundantly  giving  off  lateral  branches  with  free  terminations. 
The  extreme  cornu  of  the  pulp  is  not  supplied  with  nerves. 
(For  illustrations  of  this  condition  see  Figs.  113  and  114.) 


FIG.   113.  FIG.   114. 

FIGS.  113  and  114. — Longitudinal  sections  of  the  teeth  of  Gobius.  Golgi's 
stain.  D.  Dentine;  N.  Nerve  fibres,  ending  in  free  terminations,  close  under  the 
dentine.  (After  Retzius.) 

((3)   In   Reptilia 

Retzius  was  able  here,  to  trace  the  nerves  quite  easily,  still 
using  Golgi's  method.  In  Lacerta  agilis  he  describes  them  as 
rising,  in  the  first  place,  from  the  middle  of  the  pulp.  He  writes 
(pp.  65  and  66,  Vol.  iv).  "In  the  pulp  may  be  seen  the  con- 


146 


THE    DENTAL   TISSUES 


nective  tissue  which  also  contains  blood-vessels,  a  black  thread 
apparently  consisting  of  nerve  fibres  matted  or  closely  pressed 
together.  This  thread  rises  upwards,  and  gradually  gives  off 


FIG.   115. — Longitudinal  section  of  tooth  of  a  larva  of  the  Salamander  maculata. 
Golgi's  stain.     N.  Nerve  fibre.      (After  Retzius.) 

branches  which  extend  partly  towards  the  side,  and  partly 
upwards.  These  enter  the  odontoblast  layer,  and  pass  between 
the  cells,  as  a  rule,  to  the  upper  surface  of  the  pulp,  there  to  end 


THE   DENTAL   PULP 


147 


FIG.  1 1 6. — Tooth  of  larva  of  Salamander  maculala  with  the  surrounding  oral 
mucous  membrane.  Golgi's  stain,  x.  Amyelinic  nerve  fibre,  branching  and  end- 
ing free  in  the  pulp;  p.  Nerve  fibre  in  the  circumdental  tissues,  ending  free  in  E.  the 
surface  epithelium.  (After  Retzius.) 


148  THE    DENTAL   TISSUES 

directly  under  the  dentine  in  free  extremities,  which  here  and 
there  are  swollen  into  knots.  In  transverse  section  these  fibres 
penetrate  the  odontoblast  layer,  and  reach  the  inner  surface  of 
the  dentine,  there  to  end  free  after  a  short  ramification.  The 
penetration  of  nerve  fibres  into  the  dentine  was  nowhere 
observed." 

The  larvae  of  Salamander  Maculata  and  Triton  Cristatus 
provided  suitable  material  for  further  tracing  the  amyelinic 
nerve  fibres.  In  these  preparations,  after  their  entrance 
into  the  pulp,  the  nerves  divide  dichotomously,  and,  branch- 
ing upwards,  end  partly  in  the  side  of  the  pulp  tissue,  and 
partly  close  under  the  surface  of  dentine.  The  fine  varicose 
branchlets  rise  about  half-way  up  the  tooth,  but  never  pass  to 
the  upper  end  of  the  pulp  (p.  41,  Vol.  v.).  "All  branches  end 
freely,  spreading  out  in  different  parts  of  the  pulp.  Most  of 
them  apparently  end  close  under  the  dentine  or  near  its  inner 
surface,  but  never  penetrate  into  its  substance  or  into  its  canals." 


(7)  In  Mammalia 

The  precise  method  by  which  the  sensory  nerves  finally 
terminate  in  the  pulp  of  the  teeth  of  man,  constitutes  one  of 
those  histological  puzzles  which  yet  remain  unsolved;  and 
even  to-day,  it  is  absolutely  impossible  to  give  a  clear  and  proved 
solution.  As  has  already  been  hinted,  the  subject  is  too  vast 
to  do  more  than  mention  the  chief  modern  theories  connected 
with  it. 

i.  In  the  teeth  of  young  mice,  Retzius  in  1894  (op.  cit.  Vol. 
vi.,  p.  64)  succeeded  in  staining  the  nerve  fibres,  not  only  every- 
where in  the  pulp,  from  the  beginning,  near  the  blood-vessels, 
but  also  in  tracing  their  branches  into  the  odontoblast  zone, 
and  between  these  cells  to  the  under  surface  of  the  dentine. 
"In  vertical  sections  the  fibres,  like  a  string  of  tiny  beads, 
stretch  between  the  odontoblasts  to  the  surface  and  there  end 
free."  They  often  bend  round  on  reaching  the  surface,  and 
run  a  little  way  tangentially.  In  a  tangential  section  they  can 
be  partially  traced  under  the  dentine." 


THE    DENTAL   PULP 


149 


2.  Franz  Boll,1  over  fifty  years  ago,  observed  fine  fibres 
(which  he  thought  were  nerves),  by  means  of  ^2  Per  cent, 
solution  of  chromic  acid,  in  the  pulps  of  rabbits  and  guinea-pigs. 


FIG.  117. — A  vertical  section  through  the  tooth  of  Lacerla  agilis.  Golgi's 
stain.  D.  Dentine;  o.  Odontoblasts;  p.  Pulp  with  blood-vessels  and  x.  Nerves 
which  branch,  penetrate  between  the  odontoblasts,  continue  their  ramifications 
to  the  upper  surface  near  the  dentine,  and  there  terminate.  (After  Retzius.) 

He  used  the  persistently  growing  teeth.  He  traced  them  to 
places  between  the  odontoblasts,  and  even  between  the  dentinal 
processes  of  the  odontoblasts  which  had  been  detached  from  the 

1  " Untersuchungen  iiber  der  Zahnpulpa."  Archiv.fiir  Mikroskop.  Analomie, 
Vol.  iv.,  p.  73,  1868. 


THE    DENTAL   TISSUES 


dentine.  Thus  he  believed  that  the  nerve  fibres  extend  into  the 
dentinal  tubules.  The  nature  of  the  fibres  first  described  by 
Boll  was  most  uncertain,  and  did  not  present  the  gemmules  or 


FIG.  118.  FIG.  119. 

FIG.  1 1 8. — Transverse  section  of  tooth  of  Lacerta  agilis.  Golgi's  stain. 
D.  Dentine;  o.  Odontoblast  layer;  N.  Nerve  fibre  which  passes  free  to  the  upper 
surface  of  the  odontoblast  layer  and  there  terminates.  (After  Relzius.) 

FIG.  119. — Vertical  section  of  the  upper  part  of  a  young  tooth  of  a  mouse 
five  days  after  birth.  Golgi's  stain.  E.  Enamel  with  the  ends  of  the  dentinal 
tubes  projecting  into  it;  D.  Dentine  with  stained  dentinal  tubes;  O.L.  Odonto- 
genetic  zone;  o.  Odontoblast;  N.  Amyelinic  nerve  fibre  passing  between  the  odonto- 
blasts.  (After  Retzius.) 


FIG.  120.  FIG.  121. 

FIG.  1 20. — Vertical  aspect  of  odontoblasts  having  between  them  two  ulti- 
mate branches  of  a  fine  varicose  nerve  fibre.  From  the  pulp  of  a  molar  tooth 
of  a  rabbit.  Prepared  by  staining  with  methylene  blue  fixing  in  ammonium 
molybdate  and  mounting  in  balsam.  (After  Huber.) 

FIG.   121. — Similar  to  the  preceding  figure.     Odontoblasts  seen  end  on.     The 
nerve  termination  lies  over  the  cells.      (After  Huber.) 

beads  which  Golgi's  and  methylene-blue  methods  of  staining 

depict  upon  the  axones. 

3.  Carl  Huber,1  of  the  University  of  Michigan,  made  use 
1  "The  Innervation  of  the  Tooth-pulp."     The  Dental  Cosmos,  vol.  xl.,  pp.  803 

etseq.,  1898. 


THE    DENTAL    PULP  151 

of  the  mandibular  canines  and  molars  of  dogs,  cats,  and  rabbits. 
His  most  satisfactory  results  were  obtained  from  the  pulps  of 
rabbits'  molars.  The  method  of  staining  he  employed  was 
i  per  cent,  methylene  blue  in  physiological  salt  solution  injected 
into  the  common  carotid  during  life.  He  describes  the  follow- 


FIG.   122. — Amyelinic  terminations  of  the  nerves  in  the  dental  pulp  of  a  dog. 
Stained  with  methylene  blue.      (After  Huber.) 

ing  interesting  histological  revelations: — "The  medullated,  i.e., 
myelinic,  nerve  fibres  approach  the  lower  portion  of  the  pulp 
in  one  or  several  relatively  large  nerve  bundles.  On  reach- 
ing the  lower  surface  of  the  pulps,  these  larger  bundles  break 
up  into  numerous  smaller  ones,  the  latter  consisting  of  eight 
to  ten  nerve  fibres,  although  larger  ones  are  frequently  met 


152  THE    DENTAL   TISSUES 

with.  In  the  fibrous  tissue  membrane  which  covers  the  under 
surface  of  the  pulp,  and  which  is  continuous  with  the  periodontal 
membrane,  these  smaller  nerve  bundles  form,  as  the  result  of 
frequent  anastomoses,  a  plexus  of  medullated  fibres.  .  .  The 
smaller  bundles  of  medullated  nerves,  coming  off  from  the 
plexus,  pass  nearly  perpendicularly  up  into  the  pulp,  into 
which  they  may  be  traced  as  small  bundles  of  medullated 
nerves,  two  to  eight  or  ten  in  number,  to  all  levels  of  the  pulps, 
some  to  the  very  tip.  .  .  .  On  approaching  the  surface  of  the 
pulp,  the  medullated  fibres  lose  their  medullary  sheath:  the  non- 
medullated  (i.e.,  amyelinic)  terminal  branches,  after  repeated 
division,  form  a  plexus  immediately  under  the  odontoblasts. 
They  branch  and  re-branch  into  long,  delicate  varicose  fibres." 
This  plexus  is  that  of  Boll,  and  Raschkow,  and  others,  but 
according  to  Huber,  it  is  "a  plexus  only  in  so  far  that  the 
varicose  fibrils  cross  each  other  in  various  directions." 

Huber's  observations  on  the  ultimate  termination  of  the 
nerves  corroborate  those  of  Retzius.  The  fibrils  given  off  from 
the  plexus  just  mentioned  as  being  present  beneath  the  odonto- 
blasts, pass  up  between  these  cells,  and  end,  as  fine  beads, 
usually  near  the  free  or  dentinal  end  of  the  odontoblasts.  Some- 
times they  run  tangentially.  Huber  says  that  they  do  not,  in 
his  opinion,  make  any  connection  with  the  odontoblasts,  nor 
with  any  of  the  cellular  elements  of  the  pulp:  and  he  scouts  the 
idea  of  their  entrance  into  the  dentine. 

4.  Legros  and  E.  Magitot1  examined  the  dental  pulps  of  the 
calf,  dog  and  cat,  and  concluded  that  the  terminal  filaments  are 
continuous  with  ramified  cells,  situated  immediately  below 
the  odontoblasts,  with  which  they  are  in  immediate  communi- 
cation. "There  is  thus,"  according  to  these  authors,  "a  direct 
chain  of  sensation  transmitted  from  the  nerve-ending  to  the 
dentinal  fibril  via  the  branched  cells,  and  the  basal  processes  of 
the  odontoblasts,  the  bodies  of  these  latter  and  finally  their 
peripheral  poles"  (Fig.  127.) 

The  most  careful  search  for  such  cells  in  the  pulps  of  Her- 
bivora  and  Carnivora  (including  man)  has  been  attended  only  by 
negative  results. 

1 "  Morphologic  des  follicle  dentaire  chez  les  Mammiferes."  Journal  de 
I' Anatomic  et  Physiologic,  1879. 


THE    DENTAL    PULP 

5.  Oscar  Romer,1  after  a  great  deal  of  labour  and  experiment, 
and  following  on  the  lines  suggested  by  Morgenstern,  used  the 
teeth  of  three- weeks-old  kittens,  and  adopted  the  intra-vitam 
methylene-blue  stain.  He  enunciated  the  following,  inter 
alia:— 

(i)  The  nerves  of  the  pulp  penetrate,  as  non-medullated 
filaments,  the  spaces  which  intervene  between  the  odon- 
toblasts, reach  the  zone  between  these  cells  and  the  den- 
tine, and  here  pass  into  the  interior  of  the  odontoblast 
processes,  that  is  to  say,  in  Kolliker's  dentinal  tubules. 


FIG.  123. — Diagram  of  a  section  through  the  tooth-germ  of  a  kitten,  three 
weeks  after  birth.  Prepared  by  the  intra-vitam  method  of  staining  with  meth- 
ylene  blue;  fixing  in  ammonium  molybdate,  formalin,  and  subchloride  of  plati- 
num; decalcifying  in  acetic  acid,  and  embedding  in  celloidin.  Shows  Romer's 
conception  of  the  passing  of  the  amyelinic  nerve  fibres  into  the  dentinal 
tubules.  A,  Dentinal  tubes;  O,  Odontoblasts;  N,  Fine  nerve  fibrils  going  upwards 
out  of  the  pulp,  between  the  odontoblasts  to  the  dentinal  tubules  in  the  dento- 
genetic  zone.  (After  Romer.) 

(ii)  The  chief  mass  of  the  nerve  filaments  radiate  out  of  the 
cornua  of  the  pulp  into  the  dentine;  while  the  other  zones 
of  the  dentine  of  the  crown  appear  to  be  poorer  in  nerve 
branches,  and  the  dentine  of  the  root  entirely  nerve-less. 

(iii)  A  greater  part  of  the  dentinal  tubules  widen  out  at  the 
enamel-dentine  boundary,  into  curious  partly  spindle- 
shaped,  partly  club-shaped  formations  which  are  chiefly 
arranged  in  very  great  numbers  around  the  apices  of  the 
dentinal  cusps,  and  in  which,  in  well-preserved  sections, 
small  roundish  or  larger  oval  corpuscles  are  perceptible, 

1  Loc.  cit. 


154  THE    DENTAL    TISSUES 

which  are  often  arranged  in  rosary-like  rows,  and,  with 
gold  chloride,  take  an  intense  stain;  and 

(iv)  The  small  corpuscles  in  the  interior  of  the  spindle-shaped 
enlargements  of  the  dentinal  tubes  may  be  regarded,  with 
great  probability,  as  terminal  corpuscles  of  sensitive  nerves 
in  the  dentine,  analogous  to  the  terminal  corpuscles  of  the 
sensory  nerves  of  the  skin  and  the  papillae  of  mucous 
membranes. 

This  writer,  out  of  forty-seven  drawings  in  his  monograph  gives, 
however,  only  two  figures  depicting  the  passage  of  nerves  into 
the  dentinal  tubules.  One  is  magnified  250  times,  and  the  other 
an  amplification  of  the  first,  750  times  (vide  Tafel  iv.,  Figs.  16 
and  17).  In  spite  of  their  measurements,  (0.25^  to  0.3^),  of 
his  indefatigable  zeal,  his  earnestness  and  his  precautions,  the 
author  is  unable  to  agree  with  the  interpretation  placed  upon 
the  appearances  presented  by  the  sections,  and  must  distrust 
the  drawings  accompanying  the  text.  Moreover  this  writer, 
considering  the  processes  of  the  odontoblasts  as  hollow,  describes 
sensory  nerve  fibres  as  piercing  or  passing  into  the  interiors  of 
these  cells.  This  is  entirely  erroneous,  for  nowhere  in  the  body 
do  nerve  fibres  penetrate  the  walls  and  mingle  with  the  cyto- 
plasm of  cells!  Similarly  the  work  of  Dependorf  (Deutsch. 
Monatss.  f.  Zahn,  1913)  can  be  at  once  discounted,  for  he 
describes  and  illustrates  nerve  fibres,  in  the  basis  substance  of 
the  dentine ! 

6.  Aitchison  Robertson  (op.  cit.  p.  823)  in  the  pulps  of  the  ox, 
when  treated  with  0.6  per  cent,  solution  of  potassium  anhy- 
drochromate  for  twenty-four  hours,  found  long  central  proc- 
esses to  the  odontoblasts,  which  he  believed  became  continuous 
with  the  nerve-fibrils.     He  says  (p.  324),  "The  long  central 
process  seems  to  become  the  axis-cylinder  of  a  nerve  fibre  which 
gradually  acquires  a  primitive  sheath,  in  which  the  medullary 
or  white  substance  slowly  accumulates  till  an  ordinary  medul- 
lated  nerve  results."     His  drawings,  reproduced  in  Figs.  104 
and  105,  unfortunately  convey  nothing  to  the  enquiring  mind, 
and    certainly    if    they    are    correct,    his    assumption   is   still 
unproved. 

7.  Kolliker  in  1860  (op.  cit.  p.  300)  in  the  teeth  of  man, 


THE    DENTAL    PULP 


155 


observed  that  the  primitive  fibres,  which  are  given  off  from  a 
rich  plexus,  "form  very  evident  loops,"  but  he  did  not  consider 
them  the  ultimate  terminations. 

8.  In   specimens   of  full-term  foetuses,  presumably  Human, 
Bodecker1   using   gold   chloride,   positively   asserts   "that   an 


NK 


FIG.  124.  FIG.  125. 

FIG.   124. — Longitudinal   section   of   the   dentine   of   a   young   Human   tooth. 
Stained  with  osmic  acid.     A.  Axon;  N.K.  Xerve  corpuscle.      (After  Morgenstern.) 
FIG.   125. — Nerve    ending  in   enamel   of   a  young   tooth,     s.    Xerve   corpuscle; 
A.  Axon.      (After  Morgenstern.) 

indirect  connection  of  the  two"(dentinal  fibrils  and  nerve 
endings)  "is  established  by  the  intervening  reticulum  of  living 
matter." 

It  must  not  be  forgotten,  however,  that  this  author  believes 
that  the  dentinal  fibrils  arise  between  the  odontoblasts,  whose 

1  "The  Anatomy  and  Pathology  of  the  Teeth,"  1894. 


156  THE    DENTAL    TISSUES 

role  it  is  to  furnish  the  basis-substance  of  the  dentine.  But 
this,  as  well  as  many  other  matters  of  which  Bodecker  has 
written,  must  be  accepted  with  the  greatest  caution.  His 
views  are  so  heterodox,  and  do  not  conform  in  any  degree 
with  the  accepted  hypotheses  and  observations  of  a  great 
number  of  reputed  histologists  of  various  nationalities. 

9.  Morgenstern1  describes  in  the  teeth  of  man,  bundles 
of  axones  surrounded  by  their  medullary  sheaths  passing  into 
the  dentine  or  enamel.  In  the  former  tissue  they  traverse 
tubules,  some  of  which  are  smaller  and  others  larger  than 
the  ordinary  tubules.  Each  canal  has  in  it  two  axones  and 
they  terminate  either  (i)  at  the  cortex  of  the  dentine,  or  (ii)  at 
the  amelo-dentinal  junction,  or  (iii)  even  pass  into  the  enamel. 
In  the  first-named  locality  they  end  in  knob-shaped  structures 
which  may  be  ellipsoid  or  pyriform  in  shape  (Fig.  124).  In 
enamel  they  may  end  variously,  as  in  the  dentine,  in  elongated 
nucleated  structures  where  the  axone  (a)  passes  through 
the  entire  so-called  nerve  corpuscle  to  end  at  its  periphery 
(Fig.  125),  ()3)  terminate  on  a  nucleus  of  the  said  nerve  corpus- 
cle, or  (7)  traversing  the  entire  nerve  corpuscle,  may  wind 
itself  round  one  or  many  nuclei,  and  end  on  the  last  or  further- 
most nucleus. 

His  chief  argument  lies  in  the  fact  of  the  black  colouration 
found  in  Golgi-stained  preparations,  and  he  has  adduced  no 
proof  that  what  he  has  described  as  nerves  are  nerves.  Thus 
he  writes  (page  383  op.  cit.)  "The  nerves  which  appear  in  the 
dentine  when  treated  by  the  silver  method,  show  black  fila- 
ments of  very  varied  length  and  thickness.  Their  intense 
black  colour,  and  different  peculiarities — characteristic  of  nerves 
—leave  no  doubt  of  the  identity  of  these  fibres  with  nerve 
filaments.  In  regard  to  the  wealth  or  number  of  nerves,  prob- 
ably no  one  part  of  the  tooth  is  materially  distinguished  from 
another.  There  is,  however,  probably  a  distinction  in  regard 
to  the  mode  of  their  division  and  termination.  It  is  the  dentinal 
canaliculi  which  for  the  most  part  contain  the  longer  nerve 

1"Uber  das  Vorkommen  von  Nerven  in  der  hartern  Zahnsubstanzen." 
Deutsche  Monat.  fiir  Zahnheilkunde,  p.  436,  1892;  also  Deutsche  Monat.fur  Zahn- 
heilkunde,  p.  in,  1895. 


THE    DENTAL    PULP 


157 


B  — 


N 
FIG.  126. 


N 


FIG.  127. 


FIG.  128. 


N  P 


N  S 


N 


FIG.  130.  FIG.  131.  FIG.   132.  FIG.   133. 

FIGS.  126  to  133. — To  show  in  a  diagrammatic  manner  the  various  concep- 
tions as  to  the  method  of  termination  of  the  amyelinic  nerve  fibres  in  the  pulp. 
Fig.  126,  according  to  Boll;  Fig.  127,  according  to  Magitot;  Fig.  128,  accord- 
ing to  Retzius;  Fig.  129,  according  to  Aitchison  Robertson;  Fig.  130,  according 
to  Romer;  Fig.  131,  according  to  Huber;  Fig.  132,  according  to  Pont;  and  Fig. 
J33«  according  to  the  author.  E.  Enamel;  D.  Dentine;  B.  Limit  of  pulp  tissue;  o. 
Odontoblast;  N.  Amyelinic  nerve  fibre  termination;  x.s.  Xeuron  in  spinal  cord; 
S.R.  Stellate  cells  connected  with  the  odontoblasts;  x.p.  Xerve  plexus  of  amyelinic 
fibrils. 


158  THE    DENTAL    TISSUES 

filaments:  there  occur,  however,  many  more  nerve  filaments 
than  are  in  the  dentinal  canaliculi  proper,  which  run  between 
these,  and  in  the  same  direction,  in  approximately  the  same 
direction,  and  in  quite  a  different  direction.  The  same  direc- 
tion as  that  of  the  dentinal  canaliculi  is  observed  chiefly  in  the 
crown  portion  of  the  teeth,  it  is  therefore  more  difficult  to 
distinguish  nerves  there  from  other  fibril  constituents  than  it 
is,  for  instance,  in  the  root  portions." 

Inasmuch  as  this  writer  supposed  that  myelinic  fibres 
entered  the  dentine  in  special  tubes,  and  as  these  tubes  are  non- 
existant,  his  observations  carry  no  weight  whatever. 

10.  Schafer1   accepts  Howard   Mummery's  conclusions  but 
does  not  base  his  belief  entirely  on  the  microscopical  appear- 
ances, but  on  clinical  grounds  also.     But  the  sensitiveness  of 
dentine  can  be  explained  in  other  ways  than  upon  its  supposed 
innervation. 

11.  Howard  Mummery2  has  devoted  much  patient  labour 
to  the  elucidation  of  the  nerve  terminations.     His  conclusions 
may  be  summarised  in  his  own  words,  as  follow: 

(a).  That,  in  actively  growing  teeth,  there  is  a  considerable 
supply  of  non-medullated  or  efferent  fibres  to  the  tooth  pulp, 
which  are  derived  from  sympathetic  ganglia  and  not  concerned 
in  any  way  with  the  sensitiveness  of  the  dentine,  their  ultimate 
fibrils  probably  being  distributed  to  the  coats  of  the  blood-vessels 
and  the  secreting  cells  of  the  pulp;  whether  any  fibres  of  this 
system  enter  the  dentinal  tubes  it  seems  impossible  to 
determine; 

((3).  That  at  the  cornua  of  the  tooth  pulp,  the  bundles  of 
medullated  nerve  fibers  lose  their  medullary  sheath  and  neuri- 
lemma,  and  the  axis  cylinder  expands  into  a  spreading  mass 
of  neurofibrils,  which  can  be  traced  directly  to  the  dentinal 
tubes,  which  they  enter; 

(7).  That  in  young,  growing  teeth,  these  fibres  at  the  cornua 
are  very  abundant,  and  have  a  wavy  course;  they  appear  to 

1  "Essentials  of  Histology,"  1916. 

2  "On  the  Distribution  of  the  Nerves  of  the  Dental  Pulp,"  Philos.  Trans. 
Roy.  Society,  1912;  "The  Nerve  Supply  of  the  Dentine,"  Proc.  Roy.  Soc.  Medicine, 
1912;  "The  Innervation  of  Dentine,"  Denial  Cosmos,  March,  1916,  etc. 


THE    DENTAL    PULP 


159 


consist  of  bundles  of  neurofibrils  in  many  instances,  and  these 
vary  much  in  diameter,  the  further  divisions  of  these  bundles 
probably  taking  place  in  the  tubes  of  the  dentine; 

(6).  That  at  the  lateral  portions  of  the  pulp,  the  neurofibrils 
passing  from  the  main  nerve  trunks  enter  into  an  intricate 
plexus  beneath  the  odontoblasts,  and  are  again  collected  into 
larger  strands  of  neurofibrils,  which  mostly  pass  directly  into 


B  -. 

MP 
0 


FIG.  134. — Diagram  to  show  the  method  of  termination  of  the  amyelinic 
nerve  fibres  of  the  pulp  in  the  dentine  according  to  Howard  Mummery.  E. 
Enamel;  D.  Dentine;  B.  Limit  of  pulp  tissue;  o.  Odontoblast;  N.  Amyelinic  nerve; 
P.R.  Plexus  of  Raschkow;  M.P.  Marginal  plexus;  T.  Terminations  in  dentinal  tubes 
beneath  enamel. 

the  dentinal  tubes.  They  (the  preparations)  also  demonstrate 
the  different  appearances  of  these  strands  of  fibrils,  some  being 
large  and  showing  bead-like  enlargements  at  intervals,  other 
finer  fibres  having  a  minutely  dotted  appearance; 

(e).  That  where  the  pulp  is  separated  from  the  dentine,  the 
nerve  fibres  seem  to  be  pulled  out  from  the  pulp  and  from  the 
dentinal  tubes,  and  stretch  across  the  interval,  evidently  under 
considerable  tension ; 

(f).  That  the  nerve  fibres  enter  the  dentinal  tubes  in  company 
with  the  dentinal  fibril. 


i6o 


THE    DENTAL   TISSUES 


12.  M.  Pont  in  a  contribution  to  the  Trans,  of  the  Illrd. 
International  Dental  Congress,  Paris,  1900,  on  "La  cataphorese 
en  art  dentaire  et  plus  specialement  dans  le  cas  de  dentine 


-M 


PIG.  135. — The  cornu  of  the  pulp  of  a  fully  formed  human  premolar.  M. 
Myelinic  nerve  bundle  dividing,  inclosing  the  transverse  section  of  blood- 
vessel; D.  Dentine.  Xeurofibrils  entering  the  tubules.  Prepared  and  photo- 
graphed by  J.  Howard  Mummery. 


FIG.  136. — The  cornu  of  pulp  of  erupting  human  premolar.  M.  Myelinic  nerve 
bundles  dividing;  x.  Xeurofibrils;  D.  Dentine;  B.  Blood-vessel.  Prepared 
and  photographed  by  J.  Howard  Mummery. 

hypersensible "  says:  "La  description  des  odontoblastes  rapelle 
absolument  celle  des  neurones  sensoriels  peripheriques,  et 
nous  croyons  que  les  odontoblasts  sont  des  cellules  nerveuses 


THE    DENTAL    PULP 


1 6V 


dont  les  prolongements  peripheriques  constituent  la  voie 
centripete  et  les  prolongements  pulpaires  la  voie  centrifuge." 
(''Odontoblasts  resemble  peripheral  sensory  neurones,  and  we 
believe  that  they  are  cells  of  the  nervous  system,  whose  den- 
tinal  processes  constitute  the  centripetal  poles  and  basal 
processes  the  centrifugal  poles.") 


FIG.  137. — Ameylinic  nerve  fibres  in  the  dental  pulp  of  man. 
From  a  drawing  by  the  author.  One  fibre  is  seen  approaching,  on  the 
left,  its  terminal  arborisations.  Stained  by  Dogiel's  method.  Magnified 
750  times. 


13.  For  many  years,  the  present  author  has  endeavoured  to 
demonstrate  the  ultimate  ramification  of  these  nerves.  His 
then  views  were  set  forth  at  some  length  in  the  Trans.  Odonto. 
Soc.  of  Gt.  Britain,  November,  1893.  Some  of  the  arguments 
are  reproduced  in  the  Appendix.  Since  that  communication 
appeared,  he  has  not  confined  his  investigations  to  the  pulps 


THE    DENTAL    TISSUES 


pIG  I3g — Amyelinic  nerve  fibre  in  the  dental  pulp  of  man.  Stained  by 
Dogiel's  method.  Magnified  750  times.  N.F.  Nerve  fibre  bifurcating  into  two 
terminal  branches;  N.  Nucleus  of  pulp  cell.  Photomicrograph  by  Douglas 
Gabell. 


pIG    I39 —Similar  to  Fig.  138.     The  beaded  appearance  is  well  shown.     Photo- 
micrograph by  Douglas  Gabell. 


THE   DENTAL   PULP 


FIG.  140.— Longitudinal  section  of  the  pulp  of  a  human  incisor  tooth.     Stained 
by  ford  Robertson's  modification  of  Heller's  stain.      Magnified  40  times.     Shows 
tie  general  arrangement  of  the  myelinic  nerve  bundles.     (From  a  section  prepared 
by  the  late  Storer  Bennett.) 


164 


THE   DENTAL   TISSUES 


of  the  teeth  of  man  alone,  and  has  obtained  abundant  evidences 
in  other  vertebrates  of  the  presence  of  amyelinic  fibres  at 
the  periphery  of  the  pulp.  The  photomicrograph  Fig.  109 
represents  a  teased  preparation  of  the  myelinic  fibres,  which 
go  to  form  a  component  part  of  the  plexus  of  Raschkow.  It 
was  made  thus: — A  recent  tooth,  unaffected  in  any  way  by 


FIG.   141. — The  same  as  the  preceding.     Magnified  250  times. 


morbid  influences,  on  being  carefully  split  in  the  jaws  of  a 
vise,  is  found  to  have  covering  the  inner  surface  of  the  dentine 
a  moist,  colourless,  almost  invisible  film.  Removal  of  this  and 
staining  with  suitable  reagents  revealed  a  tangled  mass  of  myel- 
inic nerve  fibres.  The  staining  reagents  used  were  not  espe- 
cially appropriate  for  amyelinic  fibres.  In  other  parts  of  the 
tissue  numerous  nerves  of  the  latter  class  could  be  readily 
stained  by  using  a  ^{Q  per  cent,  physiological  solution  of 
methylene  blue,  ''fixing"  in  picrate  of  ammonia,  and  mounting 
in  glycerine. 


THE    DENTAL    PULP  1 6^ 

As  the  result  of  his  researches,  the  author  has  the  strong  con- 
viction that  these  fibres  terminate  in  a  basket-work  of  varicose 
fibres  embracing  and  often  closely  attached  to  the  cell  walls  of 
the  individual  odontoblasts.  The  sensory  currents  are  traced, 
in  this  way,  from  the  amelo-dentinal  junction  through  the 
dentinal  fibrils,  odontoblasts,  arborisations  of  amyelinic  telo- 
dendria  to  the  myelinic  nerve  fibres  of  the  pulp. 


CHAPTER  VIII 
THE   ALVEOLO -DENTAL    PERIOSTEUM 

MICROSCOPICAL  ELEMENTS: — (i)  "Principal"  fibres;  (ii)  Connective  tissue 
fibres;  (iii)  Blood-vessels;  (iv)  Nerves;  (v)  Epithelial  masses:  (vi) 
Osteoblasts;  (vii)  Osteoclasts;  (viii)  Sharpey's  fibres;  (ix)  Calco- 
spherite  spherules. 

GENERAL   CHARACTERISTICS 

Definition. — The  thin  connective  tissue  with  extensive  vas- 
cular and  nervous  systems  which  intervenes  between  the  exter- 
nal surface  of  the  cementum  of  teeth  and  the  lamina  dura  of  the 
bone  of  their  alveolar  sockets.  Its  synonymous  terms  are: — 
"Periodontal  membrane,"  "root  membrane,"  "dental  perios- 
teum," or  "alveolo-dental  ligament."  The  expression  "Perio- 
dontal membrane"  is,  for  the  sake  of  convenience,  used  here  and 
throughout  this  work. 

Origin. — It  is  derived  from  the  outer  layers  of  the  dental 
capsule. 

Distribution. — It  exists  in  all  teeth  attached  to  the  jaws  by 
gomphosis  articulation,  viz. :  those  of  man  and  most  mammals, 
crocodiles,  and  a  few  uncommon  fish.  The  teeth  of  the  vast 
majority  of  fishes,  and  some  reptiles,  are  fixed  by  either  anky- 
losis,  hinge,  or  membrane.  In  these  the  periodontal  membrane 
is  wanting. 

The  gingival  portion  of  the  periosteum,  according  to  Stohr,1 
is  called  the  "annular  dentinal  ligament,"  or  the  ligamentum 
circulare  dentis.  This  is  entirely  incorrect,  however:  there  are 
no  tissues  specially  marked  off  from  the  others  to  form  even  a 
distant  resemblance  to  a  ligament.  No  constricting  bands  of 
strong  connective  tissue  fibres  exist  at  the  cervical  regions  of 
the  teeth. 

1  Stohr,  "Text-book  of  Histology,"  Wurzburg;  p.  112,  1914 
166 


THE    ALVEOLO-DENTAL   PERIOSTEUM  167 

Macroscopical  Appearances. — A  white  dense  membrane  cover- 
ing over  the  roots  of  teeth,  it  varies  in  thickness  in  different 
individuals,  in  different  teeth  in  the  same  mouth,  and  at  varying 
periods  of  life.  It  is  thickest  in  childhood  and  thinnest  in 
senility.  In  measurement,  in  adult  age,  it  ranges  from  350/1 
to  5OO/X  in  width,  and  from  8  to  20  mm.  in  length.  These  are 
average  statistics:  in  the  localities  where  it  dips  into  bays  or 
recesses  of  the  alveolar  process,  the  width  is  proportionately 
increased.  Its  microscopical  nature  is  best  studied  when  the 
tissue  is  retained  in  situ,  easily  accomplished  in  sections  pre- 
pared by  fixing  and  hardening  the  soft  part  first  in  formalin, 
or  Miiller's  fluid,  and  afterwards  decalcifying  with  hydro- 
chloric or  other  acids,  and  finally  cutting  on  an  ether-freezing 
microtome. 

HISTOLOGY 

The  several  parts  of  the  minute  structure  of  the  periodontal 
membrane  may  be  described  as  follows: — (i)  The  fibrous  ele- 
ments; (ii)  Cells;  (iii)  Blood-vessels;  (iv)  Nerves;  (v)  Calco- 
spherite  spherules. 

i . — The  Fibres 

The  fibrous  elements  are  grouped  into  two  separate  and  spe- 
cific divisions,  which,  however,  are  indistinguishable  anatom- 
ically:— (A)  The  "principal"  fibres,1  and  (B)  The  ordinary  and 
less  important  connective  tissue  fibres. 

A 

The  principal  fibres  of  which  the  greater  part  of  the  mem- 
brane is  composed  are  of  the  white  connective  tissue  variety,  no 
elastic  fibres  whatever  being  present  (Black).  Many  are  fas- 
ciculi of  delicate  wavy  fibrils  gathered  together  to  form  coarse. 
strong  bands;  but  more  commonly  they  run  in  loose  bundles.  At 
the  neck  of  the  teeth  they  pass  immediately  outward  from  the 
cementum, — the  fibres  generally  lying  fairly  parallel  to  each 
other,— to  be  inserted  into  the  fibrous  mass  of  gum  tissue. 

1 A  term  first  suggested  by  Black  in  "Periosteum  and  Peridental  Membrane," 
1887,  to  whom  a  great  deal  of  our  knowledge  of  the  histology  of  this  tissue  is 
due. 


1 68 


THE    DENTAL    TISSUES 


Nearer  the  radicular  portion,  the  fibres  merge  into  the  connec- 
tive tissue  fibres  of  the  periosteum  of  the  alveolus,  from  which 
they  cannot  be  readily  distinguished.  In  the  apical  region  they 
are  very  irregular,  or  may  be  almost  absent,  this  portion  of  the 
socket  of  the  tooth  being  filled  with  small  cells,  and  few  fine 
fibres  (the  " indifferent  tissue"  of  Black),  with  abundant  room 
from  the  passage  of  blood-vessels  and  nerves.  The  apical  region 


FIG.  142. — Transverse  section  of  the  periodontal  membrane  of  man  in  situ. 
Prepared  by  the  Author's  process.  Stained  with  Ehrlich's  acid  hasmatoxylene. 
Magnified  250  times.  M.  The  root-membrane  with  its  fibres  and  cells;  B.  Its 
blood-vessels;  and  E.  Its  epithelial  gland-like  bodies;  D.  Dentine;  c.  Structureless 
cementum;  A.  Bone  of  the  alveolus;  Oi.  Osteoblasts  on  the  wall  of  the  alveolus; 
02.  Osteoblasts  on  the  surface  of  the  cementum. 

may  measure  0.5  mm.  in  depth.  At  the  surface  of  the  gum  the 
fibres  course  in  wavy  lines  directly  outwards,  i.e.,  at  right  angles 
to  the  long  axis  of  the  tooth,  and  then  suddenly  upwards  to  be 
inserted  into  the  gum;  at  the  neck  of  the  tooth  near  the  alveolar 
margin  they  are  inclined  root-ward,  and  are  inserted  into  the 
bone  or  periosteum.  At  the  mid-distance — otherwise  the 
alveolar  portion  of  the  membrane, — they  run  squarely  across; 
but  near  the  apex  of  the  root,  they  assume  a  crownward  direc- 
tion. At  the  apical  region  itself  they  radiate  from  the  cemen- 
tum to  the  bone. 


THE    ALVEOLO-DENTAL    PERIOSTEUM 


169 


The  fibres  which  arise  from  the  cementum  are  finer  than  those 
inserted  into  the  lamina  dura,  and  are  continuous  with  Sharpey's 
fibres  of  the  cementum;  and  the  large  ones,  as  a  rule,  break  up 
into  delicate  bundles  of  fibrils. 

They  all  pursue  a  rather  sinuous  course,  being  deviated 
from  straight  lines  by  the  presence  of  the  vascular  and  nervous 
zones  in  the  central  portions  of  the  membrane. 


FIG.  143. — The  fibres  of  the  periodontal  membrane.  D.  Dentine;  c.  Cementum; 
F.  Fibres.  Preparation  and  photomicrograph  by  Dr.  H.  Box,  Royal  College  of 
Dental  Surgeons,  Toronto. 

B 

The  ordinary  fibres  are  found  among  the  foregoing.  They  are 
the  common  type  of  connective  tissue  fibres  with  nuclei  and 
tissue  corpuscles.  They  are  arranged  diagonally  to  the  prin- 
cipal fibres,  and  are  usually  difficult  to  distinguish,  on  account 
of  their  feeble  staining  properties. 


2. 


The  Cells 


The  cellular  elements  are  of  several  varieties, 
(a)  The  lamellar  connective  tissue  corpuscles  are  spindle- 
shaped,  nucleated,  ramified,  and  very  prominent.     They  are 


170 


THE    DENTAL   TISSUES 


GL 


GL2 


, 
:>'' 


FIG.  144.     A  small  area  of  a  transverse  section  of  the  root  of  a  tooth,  and  a 
the    periodontal    membrane,    showing   glands.     D,    Dentine;     c.M. 
turn;  G.L.   and  c.iA  Tubular  glands  (?)  winding  among  the  fibres  of  the 
ibrane.      (Photomicrograph  by  G.  V.  Black.) 


THE    ALVEOLO-DENTAL   PERIOSTEUM 


171 


CC 


cc 


CM 


CB 


G  L 


FIG.   145. — Epithelial  bodies  in  the  periodontal  membrane.     C.M.  Cementum: 
C.B.  Osteoblasts  lying  between  the  fibres  of  the  membrane  close  to  the  cementu: 
G.L.   Epithelial  cells  with  nuclei;  c.C.  Connective  tissue  cells.      (Photomicrograph 
by  G.  V.  Black.) 


172 


THE    DENTAL   TISSUES 


called  "fibroblasts"  by  Black.     They  are  freely  distributed  to 
all  parts  of  the  membrane. 

These  cells,  or  corpuscles,  differ  in  no  essential  particular  from 


FIG.  146. — Showing  gland-like  epithelial  bodies  lying  between  the  large 
white  fibres  of  the  root  membrane.  D.  Dentine;  C.M.  Cementum;  C.B.  Osteo- 
blasts;  GLi;  GLJ,  Glands  (?);  F.  Large  white  connective  tissue  fibres.  (Photomicro- 
graph by  G.  V.  Black.) 

the  ordinary  cells  or  corpuscles  of  connective  tissues  generally. 
Thus,  they  are  nearly  always  of  the  flattened  or  lamellar  pattern. 
They  are  frequently  affixed  to  the  surfaces  of  the  peripheral 
fibres;  may  extend  between  several  fasciculi;  and  are  most  com- 


THE   ALVEOLO-DENTAL   PERIOSTEUM  173 

monly  joined  by  means  of  branching  processes,  which  in  this 
manner  form  delicate  reticula  throughout  the  tissue  between  the 
principal  fibres. 

They  are  composed  of  clear  granular  protoplasm,  and  their 
nuclei  are  oval  or  fusiform  in  shape.  They  may  be  well  shown 
by  staining  the  membrane  in  situ  with  chloride  of  gold  imme- 
diately after  extraction,  stripping  from  the  surface  of  the 
cementum,  and  teasing-out  pieces  thus  removed  in  a  plane 
parallel  to  the  periphery  of  the  root. 

(/3)  Osteoblasts  are  flattened,  cubical,  or  irregularly  shaped 
nucleated  cells  applied  intimately  to  the  external  surface  of 
cementum  and  bone.  This  irregularity  in  shape,  in  the  former 
situation,  according  to  Noyes  ("  American  Text  Book  of  Opera- 
tive Dentistry,  p.  144,  1901),  is  caused  by  these  cells  "fitting 
around  the  attached  fibres  of  the  membrane,  so  as  to  cover  the 
entire  surface  of  the  membrane  between  the  fibres."  They  are 
called  "cementoblasts"  by  Black,  Noyes  and  others;  but  no 
points  of  morphological  difference  can  differentiate  them  from 
those  ordinary  osteoblasts  which  are  found  in  the  inner  layer  of 
the  periosteum  of  the  alveolar  bone.  This  being  the  case, 
it  is  advisable  to  delete  the  word  "cementoblast"  from  dental 
terminology. 

(7)  Osteoclasts,  or  myeloplaxes,  are  multi-nucleated  giant 
cells,  oval  in  shape,  being  found  where  absorption  of  either  bone 
or  cementum  is  in  progress.  They  measure  30^  in  diameter, 
and  are  most  frequently  discovered  in  the  bay-like  recesses 
(the  foveolae  of  Howship)  on  the  periphery  of  these  hard  tissues. 
In  the  periodontal  membrane  they  lie  in  close  contact  with 
the  surface,  which  they  are  about  to  absorb,  and  thus,  while 
intervening  in  the  interfibrous  spaces,  destroy  or  cut  oil  the 
ends  of  the  principal  fibres,  when  they,  as  Sharpey's  perforating 
fibres,  are  built  into  the  bone  or  cementum. 

(5)  Epithelial  cellular  bodies  or  "rests"  are  not  infrequently 
observed  in  the  inner  portion  of  the  periodontal  membrane. 
They  appear  near  the  cementum,  just  outside  the  layer  of  osteo- 
blasts, and  are  seen  exceedingly  well  in  horizontal  sections. 
Very  pronounced  are  they  in  the  root  membranes  of  the  teeth 
of  the  sheep  and  pig,  less  so  in  man,  except  in  the  teeth  of 


!74  THE   DENTAL   TISSUES 

the  young.  Attention  was  originally  attracted  to  these  masses 
by  Malassez1  in  1885;  and  Black  described  and  figured  them 
in  "Periosteum  and  Peridental  Membrane,"  1887;  but  in 
ascribing  to  them  the  role  of  lymphatics,  he  was  probably 
incorrect,  as  no  true  lumina  have  ever  been  discovered,  and 
their  connection,  if  any,  with  the  hypothetical  lymphatic 
system  has  never  been  traced.  This  worker  has,  however, 
modified  his  views  on  their  functions  and  character  in  his 
latest  addition  to  the  literature  of  the  subject  (The  Dental 
Cosmos,  p.  101,  1899). 

Most  probably,  whatever  be  their  functions,  they  take  their 
origin  from  scattered,  unabsorbed,  or  unatrophied  remnants 
of  the  epithelial  sheath  of  Hertwig,  as  was  first  pointed  out 
by  von  Brunn,2  or  from  vestigial  remains  of  the  tooth-band, 
which  have  persisted  after  disappearance  of  that  structure. 

Under  magnifications  of  250  diameters,  their  histological 
characteristics  can  be  easily  discerned  in  suitably  stained  cases.3 

Situated  between  the  principal  fibres,  and  running  generally 
in  an  outward  direction,  they  assume  the  form  of  cords  or 
tube-like  collections  of  epithelial  cells,  each  of  which  contains 
in  the  centre  a  large  oval  nucleus.  Surrounding  each  "rest" 
is,  apparently,  a  very  delicate  basement  membrane.  Cut 
obliquely,  there  is  some  trace  of  what  might  be  a  lumen;  but 
the  glandular  nature — or  otherwise — of  these  bodies  as  described 
by  Black  requires  more  investigation  and  confirmation  before 
dogmatic  statements  as  to  their  real  character  can  be  expressed. 

Regarding  the  so-called  "gingival  gland,"  Black  writes  as 
follows:  "This  is  a  small  lobulated  mass  of  connective  tissue 
cells  lying  close  to  the  attachment  of  the  gum  to  the  tooth  at 
the  gingival  line.  It  is  mostly  included  within  the  prolongations 
of  the  epithelium  of  the  gingival  trough,  or  that  which  covers  the 
portion  of  the  free  margin  of  the  gum  lying  next  to  the  neck  of 
the  tooth.  It  has  a  strong  glandular  appearance.  Its  cellular 
elements  are  not  epithelial,  but  are  round  connective  tissue  cells. 

l"On  the  Existence  of    Masses  of    Epithelium  round  the  Roots  of  Adult 
Teeth,  in  a  Normal  State."     Journal  of  the  Brit.  Dent.  Association. 
2  Archiv.  fur  Mikroskop.  Anatomic,  1887. 
3  Haematoxylene  is  a  useful  reagent. 


THE   ALVEOLO-DENTAL   PERIOSTEUM 


DT 


D  T 


FIG.  147.— Supposed  duct  of  glands  of  the  root  membrane,  starting  from  a 
group  of  glands  not  shown  in  the  field.  C.M.  Cementtim;  D.T,,  D.TJ,  D.TS,  Uuct; 
F.  Fibres  of  the  membrane;  B.L.  Blood-vessels.  (Photomicrograph  by  G.  I  .  /> 


1 76 


THE   DENTAL   TISSUES 


EPL 


SG 


N  M 


EP 


CM 


G  L- 


FIG.   148.      The  so-called  "gingival  gland."      s.G.  S.G.  Gland;  C.M.  Cementum 

irted  from  the  dentine;  N.M.    Nasmyth's  membrane  separated  from  the  enamel 

he  acid  used  in  decalcification;  E.P.L.   Epithelial  column  dividing  the  gland 

trorn   the   surrounding  tissues;   except  at  its  base;   E.   Epithelial  cells;   E.P.   Epi- 

lium  of  outer  portion  of  free  margin  of  the  gum;  G.L.   Glands  of  root  membrane; 

ict  leading  from  glands  towards  the  gingivus;  D.TS.   Small  loop  of  second 

ict;  F.  Fibrous  tissue  of  the  gum.      (Photomicrograph  by  G.  V.  Black.) 


THE    ALVEOLO-DENTAL    PERIOSTEUM  177 

These  are  in  lobules,  divided  in  part  by  delicate  hyaline  mem- 
branes, which  often  appear  double  in  sections,  occasionally 
giving  the  appearance  of  ducts.  But  close  studies  of  them 
indicate  rather  that  they  are  duplicatures  of  the  membrane 
envelope.  In  part,  the  lobules  are  divided  by  epithelial  bands 
from  the  prolongations  of  the  epithelium  of  the  gingivse.  A 
strong  epithelial  band  from  the  gingival  epithelium  encircles  the 
whole  mass  and  parts  it  from  the  neighbouring  tissues  except 
at  its  base.  In  cross-sections  this  epithelial  band  is  seen  to  be  a 
continuous  sheet  without  break.  Though  definitely  lobulated, 
this  body  does  not  seem  to  possess  the  character  of  a  gland, 
and  I  should  not  suppose  from  an  examination  of  this  tissue 
that  it  had  a  glandular  function.  It  encircles  but  a  portion 
of  the  neck  of  the  tooth,  usually  only  the  approximal  portion, 
thinning  away  towards  the  buccal  or  lingual,  so  that  in  many 
of  the  lengthwise  sections  it  may  be  very  small  or  does  not 
appear  at  all." 

3.  The  Vascular  System 

This  lies  in  the  central  zone  of  the  tissue  and  is  fairly  abun- 
dant. Arterial  branches  having  a  common  origin  with  those  of 
the  pulp  pass  towards  the  crown  from  the  apical  region.  Run- 
ning thence,  they  branch,  divide,  and  subdivide  and  are  freely 
distributed  through  the  body  of  the  membrane,  meeting  and 
inosculating  with  the  vessels  of  the  gum  and  periosteum,  and 
even  occasionally  of  the  Haversian  systems  of  the  alveolar 
bone. 

The  capillary  network  is  scanty,  the  blood  supply  of  the 
membrane  being  chiefly  arterial  and  venous.  Of  the  former 
the  largest  vessels,  in  horizontal  section,  may  measure  0.05 
mm.  to  o.i  mm.  in  diameter. 

The  veins  accompany  the  arteries. 

4.  The  Nervous  System 

The  exact  manner  of  the  distribution  and  nature  of  the  ulti- 
mate terminations  or  ramifications  or  anastomoses  of  the 
nervous  supply  of  the  root  membrane  is  unknown:  it  is  a  branch 
of  Dental  Histology,  which  so  far  has  been  practically  ignored. 


178  THE   DENTAL   TISSUES 

According  to  Noyes,  however,  "six  or  eight  myelinic  fibres 
enter  the  apical  region  in  company  with  the  blood-vessels, 
and  they  receive  other  trunks  through  the  walls  of  the  alveo- 
lus and  over  the  border  of  the  alveolar  process"  (Op.  cit.  p.  155). 

5.  Calcospherite  Spherules 

Tiny,  almost  structureless,  rounded  masses  of  calcoglobulin, 
called  calcospherite  spherules,  may  occasionally  be  found  near 
the  epithelial  bodies.  They  are  more  constant  in  inflammatory 
conditions  of  the  membrane  (q.v.}. 


PLA.TE  11 


Two  Phases  of  Dental  Histogenesis  in  Mammalia. 


DESCRIPTION  OF  PLATE  II 

FIG.  A.— Sagittal  section  through  the  mandible  of  a  pup  at  birth.  Fixed, 
hardened  and  decalcified.  Cut  on  an  ether-freezing  microtome. 

i,  Dentine  papilla;  2,  Dentine;  3,  Enamel;  4,  Enamel  organ;  5,  Part  of  dental 
capsule;  6,  Alveolus  of  jaw  forming  the  socket  of  the  tooth;  7,  Mandibular  canal. 
A.  Ameloblasts;  B.  Stratum  intermedium;  c.  Stellate  reticulum;  D.  External  epithe- 
lium; E.  Mandibular  artery;  F.  Mandibular  veins;  G.  Mandibular  nerve. 

FIG.  B. — Lateral  half  of  coronal  section  through  mandible  of  a  foetal  rat. 
Prepared  similarly  to  preceding  Figure. 

i,  Dermal  structures  on  under  surface  of  jaw;  2,  Muscle  fibres;  3,  Muscle  fibres 
of  tongue;  4,  Lingual  papillae;  5,  Salivary  gland;  6,  Nerve  bundles;  8,  Root  of 
incisor  tooth  cut  through;  9,  Molar  tooth;  10,  Muscle  fibres.  A.  Hairs  cut  trans- 
versely; B.  Hairs  cut  obliquely;  c.  Enamel  organ  of  incisor  tooth;  D.  Tooth-band; 
E.  Enamel  organ;  F.  Enamel;  G.  Dentine;  H.  Odontoblasts. 


PART  II 

THE  ORAL  TISSUES 


CHAPTER  IX 

THE  ORAL  CAVITY  AND  ITS  ACCESSORIES 

MICROSCOPICAL  ELEMENTS  OF  THE:  (i)  Lips  and  cheeks;  (ii)  Tongue;  (iii) 
Salivary  glands;  (iv)  Hard  and  soft  palate;  (v)  Palatine  tonsils. 

THE    LIPS   AND    CHEEKS 

These  consist  for  the  most  part  of  muscular  tissue,  which  is 
freely  supplied  with  blood-vessels  and  nerves.  Loose  areolar 
tissue,  fat  lobules,  and  great  quantities  of  minute  glands  make 
up  the  rest  of  their  substance.  Externally  they  are  protected 
by  skin,  internally  by  mucous  membrane.  This  is  studded 
everywhere  with  myriads  of  vascular  papillas  of  microscopic 
size.  In  many  papillae  nerve-end-bulbs  are  found. 

"Labial"  glands  (small  racemose  bodies)  have  the  free  ter- 
minations of  their  excretory  ducts  directed  to  the  inner  surface 
of  the  lips,  "buccal"  and  "molar"  glands  to  that  of  the  cheek, 
while  small  sebaceous  glands  occur  in  the  outer  part  of  the  red 
border  of  the  lips. 

The  mucous  membrane  of  the  mouth  generally  is  lined  with 
epithelium  of  the  stratified  squamous  variety,  many  "spiny" 
cells  lying  in  the  deeper  layers. 

THE    TONGUE 

The  tongue  is  a  large  soft  organ,  flattened  from  above  down- 
wards, situated  in  the  floor  of  the  mouth. 

It  consists  mainly  of  muscles,  extrinsic  and  intrinsic,  the 
latter  being  those  placed  entirely  in  its  substance.  The  fibres — 
striated  and  voluntary — exhibiting  the  usual  features  of 
striped  muscular  tissue  generally,  run  in  various  directions, 

181 


182 


THE    ORAL   TISSUES 


so  that  in  any  and  every  section,  some  are  cut  longitudinally, 
some  vertically,  others  transversely,  thus  forming  particularly 
attractive  preparations  for  the  microscope. 

Greater  interest  than  that  of  the  histology  of  the  muscles, 


FIG.  149. — Coronal  section  of  the  tongue  of  a  dog.  Prepared  by  hardening 
in  alcohol.  Stained  with  haematoxylene  and  cosine.  Magnified  12  times, 
s.  Superior  surface  or  dorsum  of  tongue;  c.  The  epithelium  of  the  filiform  papillae; 
B.  Blood-vessels  injected  with  carmine;  i.  Inferior  surface  of  tongue. 

however,  attaches  to  the  mucous  membrane  and  its  abundant 
supply  of  eminences  or  papillae  of  varying  size  and  shape. 

The  anterior  two-thirds  of  the  dorsum  presents  on  its  sur- 
face, tip,  and  sides,  where  the  mucous  membrane  is  thin  and 
closely  adherent  to  the  muscular  layer  beneath,  enormous 
numbers  of  papillae  known  as  "filiform,"  "fungiform,"  and 


THE    TONGUE  183 

"circumvallate."     All  are  macroscopically  visible,  but  micro- 
scopically of  considerable  interest. 

HISTOLOGY 

Each  papilla  is  covered,  like  the  rest  of  the  oral  mucous 
membrane,  with  multitudes  of  secondary  papillae  closely  em- 
braced by  the  epithelium.  Each  contains  a  capillary  loop,  and 
plexus  of  nerves. 


FIG.  150. — Vertical  section  of  tongue  of  man.  Prepared  in  the  usual  way. 
Stained  with  haematoxylene.  Magnified  70  times.  F.  Conical  papilla;  s. 
Secondary  papilla;  H.  Epithelium  of  laminated  structure  between  the  papilla?, 
and  extended  into  ciliform  processes  over  it.  L.  Tunica  propria;  v.  Muscle 
fibres  cut  vertically;  T.  Muscle  fibres  cut  transversely. 

As  already  stated,  the  papillae  are  of  three  kinds: — 
i.  The  conical  papilla  abound  all  over  the  dorsum,  but  are 
absent  from  the  base  of  the  tongue.  In  shape  they  are  tiny 
elevations  with  tapering  or  cone-shaped  extremities.  They 
are  the  smallest  of  the  three  varieties,  measuring,  in  man,  to 
the  base  of  the  mucous  membrane,  0.9  mm.  to  i.o  mm.  in  length. 
Their  secondary  papillae  are  peculiar  and  unique  in  containing 


184  THE    ORAL   TISSUES 

great  quantities  of  elastic  fibres,  and  being  clothed  by  special 
epithelium  of  a  cornified  nature,  which  "forms  a  separate  horny 
process  over  each  secondary  papilla,  greater  in  length  than  the 
papilla  which  it  covers"  (Schafer). 

When  a  bundle  of  these  thread-like  projections  exists  over 
the  conical  papillae  (which  are  often  quite  devoid  of  them),  the 
term  "filiform"  is  employed  to  designate  the  character  of  the 
papillae.  They  are  easily  found  on  the  surface  of  the  tongues 
of  cats  and  other  carnivorous  animals. 


•  ••     !•         I        — 

FIG.  151. — Fungiform  papillae  with  gustatory  cells  of  tongue  of  rabbit.     Stained 

with   rarrmniv        \Tacmifi^rl    -?n  timoc 


with  carmine.      Magnified  30  times. 

2.  The   fungus-shaped   elevations   which   beset   the   middle 
and  fore  part  of  the  tongue  are  called  fungiform  papilla.     In 
the  recent  state  they  are  of  a  bright  red  colour.     Possessing 
blunt    rounded    extremities,    they    are    attached    by    narrow 
foundations. 

3.  Most  interesting  of  all,  are  the  circumvallate  papilla,  so 
called  from  their  environment.     Each  is  placed  in  a  poculiform 
depression  of  mucous  membrane,  and  has  a  cone-shaped  ap- 
pearance, surrounded  as  it  is  by  a  trench  or  fossa,  on  the 
outer  free  margin  of  which  is  a  slight  elevation  of  mucous 


THE    TONGUE 


l8s 


membrane.     This,    completely    circling    the    papilla,    is    the 

vallum,  which  is  comparable  to  a  rampart.     Hence  the  name. 

These  papillae  are  very  few  in  number,  sometimes  not  more 

than  a  dozen  existing  on  one  tongue.     They  are  located  on 


FIG.  152. — Circumvallate  papilla  of  the  tongue  of  man.  Prepared  in  the 
usual  way.  Stained  with  haematoxylene,  and  counter-stained  with  cosine. 
Magnified  30  times,  p.  Circumvallate  papilla  (its  epithelium);  F.  Fossa;  v. 
Vallum;  D.  Duct  of  gland  opening  into  base  of  fossa;  c.  Coriuni  of  papilla. 

the  posterior  third  of  the  organ,  arranged  in  two  rows,  which 
meet  together  at  a  point,  like  the  arms  of  the  letter  V.  In  width 
they  may  measure  as  much  as  2.5  mm.;  width  inclusive  of  the 
vallum  on  either  side  4.5  mm.  In  addition  to  the  vascular 
and  nervous  supply  of  the  corium,  the  stratified  epithelium 
which  is  extremely  thick,  contains  in  it  several  "taste  buds  or 


1 86  THE    ORAL    TISSUES 

goblets,"  both  on  the  sides  of  the  papilla  itself  and  in  the  mucous 
membrane  of  the  fossa.  At  the  base  of  the  fossa,  which  may 
measure  1.25  mm.  in  depth,  the  openings  of  the  ducts  of  one 
or  more  glands  can  be  seen. 

"Taste-buds"  are  oval  in  outline,  and  consist  of  a  collection 
of  narrow  and  fusiform 'gustatory  cells,  all  enclosed  by  a  single 


FIG.    153. — The    gustatory    cells    in    a  fungiform    papilla  of  the   section  photo- 
graphed in  Fig.  151.      Magnified  300  times.     G.  Goblet  or  gustatory  cells. 

layer  of  broader  fusiform  cells,  the  encasing  cells.  A  slight 
depression  in  the  lingual  epithelium  over  the  goblet  has  at  its 
base,  a  group  of  fine  trichinous  processes,  which  are  the  ter- 
minations of  these  gustatory  cells. 

The  base  of  the  tongue  contains  many  lymph  nodes  scattered 
in  diffuse  lymphoid  tissue  in  the  tunica  propria,  (collectively 
named  the  "lingual  tonsil"),  and  numerous  mucous  glands. 
The  latter  are  large  and  broad,  their  dimensions,  in  man,  being 
1.4  mm.  in  width,  and  even  3.0  mm.  in  length.  They  possess 
the  usual  histological  features  of  mucous  glands  generally 
(Fig.  162). 


THE  SALIVARY  GLANHS  187 

THE  SALIVARY  GLANDS 

The  parotid,  sublingual,  and  submaxillary  glands  secrete 
saliva. 

In  man,  the  former  is  composed  of  acini  of  serous  cells; 
the  sublingual  of  mucous  acini,  and  the  latter  of  both,  though 
the  serous  acini  preponderate.  According  to  its  secretion, 
so  do  the  histological  elements  of  each  gland  differ. 

HISTOLOGY 

They  are  compound  racemose  glands  (Fig.  158),  consisting 
of  an  aggregation  of  lobules,  each  of  which  has  a  duct  which, 
after  branching,  terminates,  on  the  one  hand  in  fine  small 
branches  into  which  the  acini  of  the  glands  open,  and  on  the 
other,  in  larger  ducts  which  ultimately  end  by  a  free  orifice 
on  the  surface  of  the  mouth.  Many  blood-vessels  ramify  in 
a  small  amount  of  loose  connective  tissue,  which  forms  the 
investment  for  the  lobules,  and  for  the  gland  itself.  In  the 
last  situation,  the  capsule  contains  ordinary  flattened  cells. 
a  few  granular  plasma-cells,  lymph  corpuscles,  and  occasionally 
a  little  adipose  tissue. 


Histologists  arbitrarily  divide  the  ducts  into  an  intralobular 
part  and  an  intercalary  part.  The  intralobular  portions,  larger 
than  the  rest,  and  near  the  free  opening  of  the  duct,  are  lined 
with  epithelium  of  which  the  cells  have  the  following  charac- 
teristics:— They  are  large,  columnar  or  conical  in  shape,  with 
their  truncated  extremity  directed  towards  the  lumen:  they 
have  a  centrally  placed  spherical  nucleus:  they  are  granular 
at  their  inner  and  finely  striated  at  their  outer  extremities 
(see  diagram,  Fig.  159). 

The  fibrillated  markings  are  well  seen  in  the  submaxillary 
gland. 

The  large  ducts  are  covered  with  a  coating  of  fibrous  and 
elastic  tissue,  intermingled  with  a  few  small  involuntary  muscular 
fibres. 


1 88 


THE    ORAL   TISSUES 


The  intercalary  portions,  shorter  and  narrower  than  the  pre- 
ceding, extend  to  the  acini,  and  are  lined  with  clear  flattened 
cells,  possessing  elongated  nuclei,  at  their  most  distal  part. 
As  they  approach  the  intralobular  ducts,  their  lumina  are  lined 


FIG.  154.— Vertical  section  through  base  of  the  tongue  of  man.  Prepared 
by  hardening  in  3  per  cent,  nitric  acid,  and  subsequently  staining  with  methylene- 
blue.  Magnified  25  times.  G.  Mucous  gland;  D.  Duct  of  gland  opening  on  to 
the  surface;  p.  Conical  papilla;  M.  Muscle  fibres. 

with  cubical  cells  with  small  nuclei  (see  Figs.  159  and  160). 

Acini 

The  acini  constitute  the  secreting  part  of  the  glands,  and 
are  of  two  kinds:  (A)  mucous,  and  (B)  serous. 


THE    SALIVARY   GLANDS  189 

A 

Mucous  Acini 

Bounded  by  a  delicate  reticulated  basement  membrane, 
each  acinus  is  lined  by  a  single  layer  of  true  secreting  cells. 
These  vary  according  to  their  activity  or  passivity. 

In  the  latter  condition  they  are  large,  clear,  granular,  and 
spheroidal  in  shape,  and  nearly  fill  the  whole  of  the  acini. 
They  take  stains  very  indifferently.  Each  nucleus,  somewhat 


FIG.  155. — Transverse  section  of  salivary  gland  of  cat,  stained  with  picric 
acid,  blood-vessels  injected  with  carmine.  To  show  its  abundant  vascular 
supply.  Magnified  30  times. 

flattened,  is  placed  near  the  basement  membrane.  The  trans- 
parent appearance  is  due  to  the  presence  of  mucin  or  mucigen. 

In  addition,  there  are  also  found  certain  marginal  cells,  the 
crescents  of  Gianuzzi  (the  demilunes  of  Hcidenhain  of  some 
authors).  They  have  semilunar  outlines,  are  small,  very 
granular,  and  stain  deeply  with  the  usual  dyes. 

In  an  active  state,  as  the  result  of  stimulation,  the  cells  stain 
readily,  become  rather  smaller  and  more  granular,  and  the 
nuclei,  now  no  longer  compressed,  occupy  the  central  parts  of 
the  cells  (see  Figs.  161  and  162). 


JQO  THE    ORAL   TISSUES 

B 

Serous  Acini 

At  rest,  these  cells,  when  properly  prepared  and  stained, 
are  granular,   with   their  nuclei  in   their   centres   completely 


FIG.  156. — Submaxillary  salivary  gland  of  man.  Prepared  in  the  usual 
way  Stained  with  Ehrlich's  acid  haematoxylene.  Magnified  20  times.  Shows 
several  lobules,  s.s.  Serous;  M.M.  Mucous;  B.  Blood-vessel;  c.  Connective  tissue 
between  the  lobules. 

obscured  by  the  albuminous  material  in  their  protoplasm. 
The  lumen  similarly  to  that  of  a  mucous  acinus  is  frequently 
totally  occluded. 

During  a  period  of  prolonged  activity,  the  cells  appear  to 


THE    SALIVARY   GLANDS 


be  shrunken,  a  few  granules  have  collected  in  their  inner 
aspects,  the  nuclei  are  clearly  revealed  and  easily  recognised, 
and  the  lumen  is  large  and  patent.  These  changes  are  depicted 
in  the  accompanying  diagrams  (Figs.  163  and  164). 


FIG.   157. — Diagram  of 
a  racemose  gland. 


PIG.    158. — Intralobuiar 
duct. 


FIG.   159. —  Mucous 
tercalary  duct. 


FIG.     160. — Serous    in- 
tercalary duct. 


FIG.  161. — Acinus  of 
a  mucous  gland  during 
a  period  of  passivity. 


FIG.  162. — Acinus  of 
a  mucous  gland  during 
a  period  of  activity. 


FIG.  163. — Acinus  of 
a  serous  gland  during 
a  period  of  passivity. 


FIG.  164. — Acinus  of 
a  serous  gland  during  a 
period  of  activity. 


HARD    AND    SOFT    PALATE 


The  histology  of  the  osseous  framework,  and  fibrous  covering 
of  the  roof  of  the  mouth  requires  but  a  brief  survey,  a  descrip- 
tion of  its  bony  structure  appearing  in  the  following  Chapter. 


HISTOLOGY 


The  bone  is  covered  with  a  thin  layer  of  periosteum  and 
mucous  membrane.  Of  the  former  nothing  need  further  be 
said,  its  character  being  similar  to  that  of  the  periosteum  of 
bones  generally;  the  latter,  however,  thrown  into  folds  (palatal 


192 


THE    ORAL    TISSUES 


ruga}  exhibits  the  same  characteristics  as  in  other  parts  of  the 
mouth,  except  that  in  these  ridges,  as  well  as  in  the  papilla 
palatina  or  incisive  pad,  the  cells  are  larger,  coarser,  and  more 
multiplied  than  elsewhere. 

The  vascular  and  nervous  supplies  are  scanty,  as  is  also  the 
number  of  mucous  glands.  Adipose  tissue  is  present  to  a  limited 
extent. 


FIG.  165. — Vertical  section  of  the  hard  palate.  Stained  with  haematoxylene 
and  cosine.  Magnified  200  times.  O.E.  Oral  epithelium,  with  surface  projecting 
as  rugae;  s.p.  Simple  papilla;  c.p.  Compound  papilla;  B.V.  Blood-vessel;  B.  Surface 
of  palate  bone;  p.  Periosteum. 

The  soft  palate  consists  of  voluntary  muscular  fibres,  and  a 
great  number  of  glands  all  clothed  with  mucous  membrane, 
which  is  covered  on  the  anterior  surface  with  stratified  squa- 
mous  epithelium,  and  on  the  posterior  surface  with  ciliated  col- 
umnar cells.  It  measures  approximately  10  mm.  in  thickness. 

The  uvula  consists  chiefly  of  voluntary  muscle  fibres  and 
compound  racemose  glands,  which  abound  in  great  numbers 
on  the  anterior  surface  of  the  soft  palate  where  they  form  an 
almost  complete  layer  under  the  squamous  stratified  epithelium. 

THE    FAUCIAL    OR   PALATINE    TONSILS 

The  tonsils  are  soft,  very  vascular  bodies  placed  between 
the  anterior  and  posterior  palatine  arches  or  pillars  of  the 
fauces. 


THE    TONSILS 


HISTOLOGY 


193 


They  are  composed  of  lymphoid  tissue  enclosed  in  a  fibre- 
elastic  capsule.  Dense  masses  of  lymphoid  cells  are  collected 
here  and  there,  and  form  the  lymphoid  follicles  of  the  tonsil. 
The  latter  are  large  oval  or  round  bodies  having  a  breadth, 
in  man,  of  1.5  mm.  and  a  length  of  3.25  mm. 


OE 


MG 


FIG.  166. — Vertical  section  of  oral  surface  of  the  soft  palate.  Stained  with 
haematoxylene  and  eosine.  Magnified  200  times.  O.E.  Oral  epithelium;  M. 
Voluntary  muscle  fibres;  M.G.  Mucous  gland;  A.T.  Adipose  tissue. 

The  framework  of  the  follicles  is  a  delicate  stroma  of  fine 
retiform  connective  tissue,  similar  to  the  white  fibres  of  areolar 
tissue.  Hence  it  contains  no  nucleated  cells  as  such,  but 
trabeculae  of  fibrous  tissue  surrounded  by  an  open  network 
of  fibres  more  or  less  densely  aggregated. 

The  cells  contained  in  these  are  lymphoid  cells,  which  re- 
semble lymphocytes.  They  differ,  however,  in  the  facts  that 
they  have  less  cytoplasm,  and  a  relatively  larger  nucleus. 

Stratified  squamous  epithelium  extends  over  the  exposed 
part  of  the  tonsil.  Opening  on  the  free  surface  of  the  organ 
are  numerous  crypts  or  clefts  into  which  the  epithelium  dips, 


194 


THE    ORAL    TISSUES 


being  continuous  all  over  except  at  the  tiny  orifices  of  a  few 
mucous  glands,  the  ducts  of  whose  acini  open  on  to  the  surface 
of  the  crypts. 


L  C 


FIG.  167. — Vertical  section  of  tonsil  of  man.  Prepared  by  fixing  and  harden- 
ing. Stained  with  haematoxylene;  counter-stained  with  cosine.  Magnified  60 
times.  L.F.  Lymphoid  follicle ;c.  Crypt  of  tonsil;  D.C.  Lymph  cells  passing  through 
the  epithelium  of  crypt;  G.  Mucous  gland;  D.  Duct  of  same,  opening  into  the  base 
of  crypt. 

Lymphoid  cells  pass  through  this  epithelial  layer  of  cells 
from  the  follicles;  become  free  and  detached  on  the  surface; 
and  mixing  with  the  saliva,  appear  as  the  so-called  "salivary 
corpuscles." 


MICROSCOPICAL  ELEMENTS  IN:  (i)  Bone  of  Canine  fossa;  (ii)  Interdental 
septa;  (iii)  Hard  Palate;  (iv)  Wall  of  Antrum;  (v)  Angle  of  Mandible; 
and  (vi)  Alveolar  process. 

The  hitherto  published  descriptions  of  the  minute  structure 
of  the  osseous  framework  of  the  lower  face  and  jaw,- — such 
structures  as  are,  in  a  word,  in  direct  anatomical  relation- 
ship and  continuity  with  the  teeth  of  man, — have  necessarily 
been  given  only  very  infrequently;  but  in  addition  to  this, 
the  descriptions  which  have  appeared  in  text-books  and  jour- 
nals have  taken  for  granted  that  the  histology  of  these  par- 
ticular bones  corresponds  with  that  of  tabular  and  irregular 
bones  in  general. 

To  make  this  contribution  complete,  a  few  forewords  are 
necessary  and  advisable. 

GENERAL    CHARACTERISTICS 

Origin. — Each  maxilla  is  probably  developed  from  one  centre 
©^ossification  as  a  membranous  bone,  at  a  spot  which  marks  the 
site  of  the  canine  tooth  germ,  external  to  the  cartilaginous 
nasal  capsule.  Each  premaxilla  is  developed  from  one  centre  of 
ossification.  Each  half  of  the  mandible,  according  to  Low 
(Proc.  Anat.  Soc.  of  Great  Britain  and  Ireland,  1905),  is  developed 
from  one — the  dentary — centre  in  membrane.  Meckel's  car- 
tilage does  not  form  bone,  except  that  it  becomes  ossified  and 
incorporated  with  the  mandible  just  below  the  lingual  side  of 
the  sites  of  the  sockets  of  the  first  and  second  incisors. 

Distribution.- — Both  forms  of  bone,  known  as  compact 
(smooth,  dense,  and  ivory-like)  and  cancellated  or  spongy 


196  THE    ORAL   TISSUES 

(rough,  open,  and  soft)  are  met  with  in  the  jaws.  The  former 
is  found  covering  each  surface  both  of  maxillae  and  mandible, 
the  latter  constituting  the  intervening  tissue,  which  in  the 
case  of  the  lower  jaw  is  similar  to  the  diploe  of  the  cranial 
bones.  The  compact  forms  a  somewhat  thicker  shell  or 
crust  on  the  external  and  internal  surfaces  of  the  mandible 
than  on  any  portion  of  the  maxillae.  Compared  with  the  bone 
of  the  sockets  of  the  teeth  of  the  mammalia  generally  —  par- 
ticularly those  of  the  hyena  —  that  of  man  is  a  degenerate 
structure,  on  account  of  the  fact  that  its  blood  supply  is  feeble 
and  inadequate,  it  serves  for  the  attachment  of  no  muscles  except 
a  few  fibres  of  the  buccinator,  and  it  is  therefore  almost  func- 
tionless,  and  rapidly  undergoes  at  its  gingival  margins  physio- 
logical absorption  or  atrophy.  (See  Appendix.) 

HISTOLOGY 

Before  considering  the  special  histology  of  the  bones  of  the 
jaws,  a  brief  description  of  the  structure  of  osseous  tissue 
generally  must  be  given. 

Bone  of  the  jaw,  as  bone  elsewhere,  consists  of  a  calcined 
fibrous  ground-substance  or  matrix  arranged  as  lamellae  around 
spaces  of  varying  shape,  size,  and  contents  which  everywhere 
penetrate  it  in  all  directions.  Of  these  the  following  are  to  be 
noted:  (a)  Haversian  systems,  (b)  lamellae,  (c)  periosteum, 
and  (b)  Sharpey's  fibres. 

(a)  An  Haversian  system  consists  of  an  Haversian  canal, 
several  lamellae,  with  numerous  lacunae  and  canaliculi. 

Interpenetrating  everywhere  are  short  longitudinal  pas- 
sages or  tubes  which  in  cross-section  appear  as  rounded  or 
oval  apertures,  and,  longitudinally  cut,  like  short,  straight, 
or  slightly  curved  spaces  of  fairly  regular  diameter  through- 
out. These  are  the  Haversian  canals.  The  largest  may  meas- 
ure loo/x  in  width,  the  smallest  20ju,  the  average  size  being  about 


They  are  surrounded  by  lamellae,—  thin  bands  of  bony 
material  arranged  concentrically  round  each  canal.  Dark 
and  light  alternate,  the  difference  in  the  refraction  being  due 
to  the  fact  that  the  opaque  lines  are  occasioned  by  the  calcified 


THE  MAXILLARY  AND  MANDIBULAR  BONES        197 

fibrils  running  longitudinally,  and  the  clear  zones  by  their 
running  transversely.  In  consequence,  the  ends  only  of  the 
fibrils  are  cut  across  (see  Fig.  176). 

Situated  between  these  lamellae  are  bone-lacunae  with  their 
canaliculi.  The  first  are  flattened  branched  spaces,  which 
may  measure  i^fj.  in  their  greatest  diameter.  In  dried  speci- 
mens they  look  like  myriads  of  tiny,  dark,  fusiform  specks 
arranged  with  fairly  uniform  regularity  between  the  lamellae, 
and  fully  connected  with  each  other  and  with  the  Haversian 
canals  by  means  of  many  long,  narrow  tubes  or  canaliculi  which 
cross  the  lamellae.  Each  cavity  is  filled  with  or  contains  a  bone- 
cell  with  a  large  oval  nucleus,  as  first  described  by  Virchow. 
These  are  homologous  with  those  of  ordinary  connective 
tissue.  The  wall  of  each  lacuna  is  formed  of  some  substance 
which  resists  the  action  of  decalcifying  reagents  in  a  similar 
manner  to  the  sheaths  of  Neumann  in  dentine. 

The  contents  of  an  Haversian  canal,  in  the  recent  state, 
comprise  several  capillaries,  small  arteries  and  veins,  a  bundle 
of  nerve-fibrils,  and  a  few  lymphatic  vessels,  all  imbedded  in 
fine  connective  tissue,  which  is  surrounded  externally  by  a 
tough  lining  membrane  possessing  properties  identical  with 
that  which  obtains  also  in  the  membranous  lining  of  the  walls 
of  the  lacunae. 

(&)  In  addition  to  the  concentric  lamellae,  others  arranged 
parallel  to  the  surface  of  the  bone,  are  called  "circumferential" 
or  "peripheric;"  while  a  third  set,  when  found  between  the 
Haversian  systems,  are  commonly  spoken  of  as  "interstitial." 
Their  structures  differ  in  no  particular  from  the  concentric 
lamellae. 

(c)  The  periosteum  can  be  well  studied  microscopically  in 
sections  where  the  hard  and  soft  parts  have  been  retained 
in  situ.     Bony  periosteum  consists  of  two  layers,  an  outer, 
made  up  chiefly  of  white  fibrous  tissue,  and  an  inner,  of  the 
same  with  few  yellow  elastic  tissue  fibres  and  capillaries  in 
addition.     In  developing  bone,  osteoblasts — small,  cubical,  nu- 
cleated cells — are  also  present  in  this  inner  osteogenetic  layer. 

(d)  Sharpey's  perforating  fibres  are  noticed  in  thin  strips 
of  decalcified  bone  near  the  surface.     They  thus  run  in  from 


198  THE    ORAL   TISSUES 

the  deep  surface  of  the  periosteum  and  pierce  the  peripheric 
lamellse  in  a  perpendicular  or  oblique  direction.  The  fibrous 
bundles  are  of  varying  lengths,  and  taper  gradually  to  their  free 
extremities.  They  are  fasciculi  of  fibrils,  probably  of  white 
fibrous  tissue;  though  it  has  recently  been  shown  that  many 
are  perhaps  elastic  fibrils.  When  they  do  not  become  calcified 
they  shrink  and  leave  tubes  in  the  channels  in  the  dry  bone. 
Sharpey  also  first  demonstrated  the  presence  of  decussating 
transparent  fibrils  which  constitute  the  main  part  of  the  lamellae 
(see  Fig.  176).  In  this  way,  in  bone,  Sharpey's  discoveries 
include  both  perforating  and  decussating  fibres,  the  former 
being  bundles  of  fibrils,  the  latter  an  exceedingly  delicate 
network  of  fibres.  In  dental  histology  Sharpey's  fibres  are  the 
fibres  which  run  from  the  periodontal  membrane  into  the 
cementum;  while  his  homologous  fibres  in  dentine  matrix 
were  originally  seen  and  described  by  von  Ebner1  and  later  by 
J.  Howard  Mummery.2 

Turning  now  to  the  minute  structure  of  several  typical 
portions  of  the  bones  of  the  jaws,  it  will  suffice  to  point  out 
their  distinguishing  features. 

(i)  Bone  of  Canine  Fossa 

In  vertical  lateral  sections  of  the  bone  of  a  young  subject 
(age  ten  and  a  half  years) ,  it  is  found  that  the  greater  part  of 
the  tissue  is  composed  of  a  dense  osseous  substance,  but  very 
scantily  supplied  with  Haversian  systems.  Large  areas  of 
bone  are  quite  devoid  of  either  lamellae,  lacunae,  or  canaliculi 
(Fig.  1 68).  The  matrix  is  distinctly  coarsely  granular  (see 
Fig.  169),  and  has  in  it  an  indefinite  number  of  short  canals, 
the  majority  of  which  do  not  always  communicate  with  lacunae. 
These  tiny  tubular  spaces,  probably  in  the  recent  state,  contain 
connective  tissue  fibrils,  as  they  are  too  minute  for  the  con- 
veyance of  blood-cells  or  even  lymph.  They  are  most  marked 
and  most  numerous  in  the  neighbourhood  of  the  lacunae,  the 
canaliculi  of  which  they  somewhat  resemble.  Varying  in 

"Handbuch  der  Zahnheilkunde,"  Vienna,  1890-91. 
2  Philos.  Trans.  Royal  Society  of  London,  1891. 


THE    MAXILLARY   AND   MANDIBULAR   BONES 


FIG.  168. — Vertical  section  of  the  bone  of  the  canine  fossa;  from  a  dried  speci- 
men. Magnified  45  times..  Unstained.  Sho%vs  its  general  histological  features. 
The'  dark  masses  are  crowds  of  lacunae,  the  lighter  portions  the  ground  substance. 


FIG.   169. — Granularity   of  the  osseous  matrix  of  the  floor  of  the  canine  fossa. 
Magnified  750  times.      Unstained. 


20O 


THE    ORAL   TISSUES 


FIG.  170. — Abrachiate  lacunae  from  a  dried  specimen  of  the  floor  of  the  canine 
fossa.  Magnified  750  times.  Unstained.  In  the  matrix  a  few  short  canals 
can  be  seen. 


FIG.   1 71 . — Vertical  section  of  the  bony  septum  between  two  maxillary  premolars. 
Magnified  40  times.      Unstained. 


THE    MAXILLARY    AND    MANDIBULAR   BONES 


2OI 


length,  their  diameter  measures  about  i/x.  Several  are  shown 
in  the  photomicrograph  Fig.  169. 

The  Haversian  lamellae,  when  they  do  occur,  are  but  feebly 
marked.  They  do  not  present  the  usual  microscopical 
characteristics  of  other  bones,  being  very  irregularly  disposed 
in  position  and  in  shape,  size,  and  constituents. 

The  lacunae  are  massed  together  without  order  or  regu- 
larity. Many  are  spherical  in  shape  and  absolutely  unlike 


LD 


LD 


FlG.  172. — Radiograph  of  left  side  of  normal  jav/s  of  man  aged  forty-five 
years,  showing  at  L.D.  the  lamina  durx.  A  certain  amount  of  absorption  of  the 
terminal  margins  of  the  alveolar  processes  has,  here  and  there,  occurred. 

those  of  well-constructed  compact  bone,  the  majority  being 
provided  with  short  coarse  offshoots,  though  great  numbers 
are  quite  abrachiate.  This  last  fact  is  of  great  interest,  and 
probably  has  also  some  pathological  significance.  These 
lacunae,  as  is  well  shown  in  Fig.  171.  do  not  possess,  and  they 
probably  never  did  possess,  canaliculi;  their  outlines  are 
sharply  denned  rounded  or  oval  contours,  and  under  low 
magnifications  rather  simulate  dentinal  tubes  cut  transversely. 


202  THE    ORAL   TISSUES 

In-  addition  to  the  granular  matrix,  the  substance  of  the 
bone,  thin  though  it  is,  contains  numbers  of  broad  channels 
of  great  length,  which  may  perhaps,  during  life,  act  as  venous 
carriers  of  the  blood  or  give  passage  to  lymphatic  vessels. 
Possessing  no  histological  or  physiological  interest,  they  occur 
sufficiently  commonly  in  this  situation  to  warrant  merely  a 
passing  reference. 


L  D 


LD 


FIG.   1 73. — Radiograph  of  right  side  of  jaws  of  man  aged  forty-five  years,  showing 
at  L.D.  the  lamina  durce. 

(ii)   The  Interdental  Septa 

These  are  composed  of  cancellated  bone  the  lattice-like 
character  of  which  differs  in  no  material  degree  from  spongy 
bone  elsewhere.  The  lamellae  are  arranged,  as  a  rule,  in 
lines  parallel  to  the  edges  of  the  large  openings  in  the  bone. 
The  lacunas  are  very  numerous;  a  few  are  abrachiate,  but  by 
far  the  greater  number  possess  canaliculi  (Fig.  171). 

Thin  sheets  of  compact  bone  exist  normally  immediately 
outside  the  periodontal  membranes  of  the  teeth.  These  are 


THE    MAXILLARY   AND    MANDIBULAR   BONES 


203 


called  Lamina  durce.     Good  radiographs  show  them  in  a  marked 
degree,  see  Figs.  172  and  173. 

In  the  recent  state,  the  large  open  spaces  in  the  bone  are 
filled  with  quantities  of  red  medullary  tissue,  viz. — -delicate 
branching,  retiform  tissue  supporting  the  marrow  cells  of 
Kolliker,  and  small  coloured  nucleated  cells  many  of  which 
undergo  sub-division  by  mitosis. 


FIG.  174. — Sagittal  section  of  the  substance  of  the  hard  palate.  Magnified 
250  times.  Unstained.  The  photograph  exhibits  the  fusiform  shape  of  the 
lacunae  in  the  lamelte,  and  the  rounder  spaces  elsewhere;  also  the  connective 
tissue  stroma  of  the  matrix. 


(iii)  Hard  Palate 

Vertical  antero-posterior  sections  of  the  roof  of  the  mouth 
at  the  articulation  of  the  palatal  process  of  the  maxillary 
with  the  horizontal  plate  of  the  palate  bones,  near  the  sutural 
line,  all  reveal  the  characteristics  of  dense  osseous  tissue 
thickly  crowded  with  lacunae  and  canaliculi  (Fig.  174),  and  also 
several  longitudinal  spaces  of  large  dimensions  filled  with 
marrow.  The  long  axes  of  the  lacuna?  are  more  or  less  parallel 
to  the  long  axes  of  the  cancelli. 


2O4 


THE    ORAL   TISSUES 


FIG.   175. — Radiating  connective  tissue  fibres  in  the  matrix  of  the  bone  of  the  wall 
of  the  maxillary  sinus.      Magnified  250  times.      Unstained. 


FIG.  176. — Perforating  fibres  running  lengthwise  through  the  matrix  of  the  bony 
wall  of  the  maxillary  sinus.  Magnified  800  times.  Unstained.  The  cut 
extremities  of  descussating  fibres  appear  as  white,  round  dots. 


THE    MAXILLARY    AND    MANDIBULAR   BONES 


205 


(iv)  Nasal  Wall  of  Antrum  of  Highmore 

Here,  as  in  the  bone  which  constitutes  the  floor  of  the  canine 
fossa,  the  matrix  is  very  coarsely  granular,  and  contains  in 
places  long  markings,  which  are  evidently  the  remains  of  the 
connective  tissue  stroma  (Figs.  175  and  176).  The  lacunas, 
which  are  exceedingly  scanty,  do  not  present  the  usual  charac- 
teristics, being  spherical  or  oval  when  viewed  from  above  (Fig. 
1 77) .  Some  are  concavo-convex  as  seen  in  side  section.  Again, 
the  canaliculi  are  but  very  indifferently  formed. 


FIG.   177. — Abrachiate  lacunae  amongst  perforating  fibres.      Bone  of  antral  wall. 
Magnified  250  times.      Unstained. 

(v)  Angle  of  Mandible 

Examination  of  the  structure  of  vertical  transverse  sections 
exhibits,  best  of  all,  the  pervious  parts  of  the  bones, — the 
regular  disposition  of  the  Haversian  systems,  and  the  peri- 
pheric  and  interstitial  lamellae.  The  first  are  not  very  nu- 
merous, and  are  seen  mainly  in  cross  section.  The  peripheric 
lamellae  are  comparatively  long,  and  the  line  of  demarcation 
between  the  individual  lamella?  very  marked  (Fig.  178).  Strong 
lines  of  calcined  connective  tissue  fibres  can  be  observed,  here 
and  there,  closely  welding  together  the  interstitial  lamellae 


206 


THE    ORAL    TISSUES 


FIG.  178. — Vertical  section  of  the  angle  of  the  mandible;  from  a  dried  specimen. 
Magnified  50  times.  Unstained.  The  section  shows  the  genefal  structure. 
At  the  upper  part  of  the  figure  the  long  peripheric  lamellae  are  seen  at  the  free 
edge  of  the  bone,  with  interstitial  lamellae  between  the  Haversian  systems.  At 
the  lower  part  of  the  figure  the  commencement  of  the  cancellous  diploe-like  portion 
is  separated  from  the  external  surface  by  the  dense  layer  of  dark  compact  bone. 


FIG.  179. — General  structure  of  the  bone  of  the  alveolus;  from  a  recent  speci- 
men. The  cancellous  spaces  and  contents  are  too  darkly  stained  to  show  any^ 
structure.  Magnified  40  times.  Stained  with  fuchsin. 


THE    MAXILLARY    AND    MANDIBULAR   BONES 


207 


FIG.  1 80. — Transverse  section  of  the  alveolus  in  situ;  from  a  dried  specimen. 
Magnified  40  times.  Stained  with  borax-carmine.  In  the  upper  part  of  the 
photograph  is  the  free  edge;  below,  the  dentine  and  cementum,  with  the  perio- 
dontal  membrane  intervening. 


FIG.   181. — Perforating  fibres  of  the  alveolus,  passing  into  the  periodontal  mem- 
brane.     Magnified  800  times.      Unstained. 


208  THE    ORAL    TISSUES 

even  in  bones  of  adult  life  (age  thirty-five  years) .  Internal  to 
the  free  surface  of  the  jaw,  the  cancellated  tissue  follows  very 
much  the  lines  already  laid  down. 

Vertical  lateral  preparations  of  the  same,  show  absence  of 
Haversian  systems,  but  multitudes  of  lacunae  and  canaliculi, 
and  many'radiating  bands  of  calcified  fibres. 


FIG.   182. — Lacunae  and  canaliculi  in  the  bone  of  the  alveolar  process,      Magnified 
250  times.      Unstained. 

(vi)  Alveolar  Process 

Here  are  found  all  the  appearances  of  soft  cancellous  bone, 
with  Haversian  systems  and  lacunae  well  marked  (Figs.  179 
and  182).  The  cancelli  run  longitudinally  in  the  same  direction 
as  the  long  axes  of  the  teeth.  Osseous  tissue  is  dense  externally 
(see  Fig.  180) ;  and  the  perforating  fibres  are  very  strong  and  of 
great  length  (Fig.  181). 

The  foregoing  remarks  refer  to  the  greater  portion  of  the 
bony  structures.  At  the  free  gingival  terminations,  however, 
the  alveolar  process  is  so  narrow,  that  there  is  no  room 
to  accommodate  medullary  spaces  and  Haversian  systems. 
These  are,  therefore,  usually  non-existent.  The  external 
alveolar  plate  is  considerably  thinner  than  the  internal  alveolar 
plate:  in  neither,  does  the  bone  exhibit  a  typical  appearance. 


CHAPTER  XI 

A  GROUP  OF  MINOR  STRUCTURES.      THE  ABSORBENT 

ORGAN— THE  DENTAL  CAPSULE— THE  GUM— THE 

LINING  MEMBRANE  OF  THE  ANTRUM   OF 

HIGHMORE 

THE    ABSORBENT    ORGAN 

MICROSCOPICAL   ELEMENTS: — (i)    Connective   tissue   stroma;    (ii)  Osteo- 
blasts;  (iii)  Foveolae  of  Howship. 

GENERAL   CHARACTERISTICS 

Definition. — A  delicate  vascular  structure  spread  over  por- 
tions of  the  roots  of  the  deciduous  teeth  of  man,  during  the 
periods  when  they  are  about  to  be  shed. 

Origin. — From  the  outer  layer  of  the  dental  capsule  of  the 
permanent  teeth. 

Macroscopical  Appearances. — A  thin,  white,  insensitive  organ 
covering  the  excavated  parts  of  the  roots  of  deciduous  teeth 
loosened  by  the  impending  eruption  of  their  permanent  suc- 
cessors. It  can  be  easily  removed  from  the  dentine,  but  is  best 
observed  and  studied  when  retained  in  situ.  It  may  also  be 
seen  as  a  soft  reddish  papilla  over  the  crowns  of  the  erupting 
permanent  teeth. 

HISTOLOGY 

Vertical  sections  exhibit  a  tissue  composed  of  cells  and  blood- 
vessels imbedded  in  a  dense  connective  tissue  stroma. 

The  cells  are  usually  small  and  round,  with  round  or  oval 
prominent  nuclei.  On  the  surface,  and  filling  the  foveolse  of 
Howship — large  bay-like  crescentic  excavations  in  the  dentine 

14  20Q 


2IO 


THE    ORAL   TISSUES 


FIG.  183. — The  absorbent  organ.  Prepared  by  the  Author's  process.  Stained 
with  Ehrlich's  acid  hasmatoxylene.  Magnified  40  times,  o.  Absorbent  organ ; 
D.  Dentine  of  the  deciduous  tooth. 


FIG.  184. — Same    as    the  preceding.     Magnified   250   times.     H.  A  Howship's 
ioveola  with  its  giant-celled  occupant;  D.  Dentine  of  the  deciduous  molar. 


THE   ABSORBENT   ORGAN 


211 


—are  found  large  multi-nucleated  giant  cells  which  correspond 
in  many  particulars  with  osteoclasts.  In  fact,  they  may  be  con- 
sidered to  be  nothing  more  nor  less  than  these  specially  organ- 
ised cells.  The  cells  which  make  up  the  main  mass  of  the 
organ  are  of  the  ordinary  variety.  They  are  not  osteoblasts, 
in  the  general  acceptance  of  the  term,  but  may  take  on  a  lime- 
depositing  function,  as  sometimes  there  are  evidences  in  physio- 
logically absorbed  roots  of  new  depositions  of  dentinal  matrix. 


FIG.  185. — The  absorbent  organ  in  situ.  Prepared  and  stained  as  in  Fig. 
153.  Shows  a  deposition  of  dentine  matrix  (with  a  few  scattered  cells  em- 
bedded in  it)  in  the  excavated  portions  of  the  dentine.  Magnified  50  times. 
o.  Absorbent  organ;  D.  Dentine  of  deciduous  tooth;  M  Dentinal  matrix  contain- 
ing nucleated  cells;  A.  Albumenoid  material  undergoing  calcification. 

In  the  two  accompanying  photomicrographs,  Figs.  186  and 
187,  it  will  be  seen  that  a  kind  of  hyaline  matrix  has  been  laid 
down,  in  the  excavated  portions  of  the  roots  of  the  deciduous 
teeth.  This  nearly  homogeneous  material  may  at  times 
present  nothing  more  than  a  coarse  granularity,  or,  at  times, 
show  a  finely  fibrillated  reticulum  with  large  round  nucleated 
connective  tissue  cells  imbedded  in  its  midst.  Both  forms 
closely  recall  those  two  kinds  of  adventitious  dentine  found  in 
the  pulp  known  as  hyaline,  and  cellular  (q.v.}.  Here,  again. 


212 


THE   ORAL   TISSUES 


is  another  remarkable  instance  of  dentinal  matrix  being  pro- 
duced without  the  aid  of  the  so-called  odontoblasts. 

The  vessels  are  very  numerous,   but  comparatively  large 
nerves  other  than  vaso-motor  branches  are  probably  absent. 


FIG.  1 86. — A  similar  section  to  the  preceding.  Prepared  and  stained  as  in 
Pig  184.  Magnified  250  times.  H.  The  foveolae  of  Howship  filled  with  cal- 
cified dentinal  matrix. 


THE   DENTAL   CAPSULE 

MICROSCOPICAL  ELEMENTS: —  (i)  Outer  and  Inner  Portions;  (ii)  Fibres; 
(iii)  Glands. 

GENERAL   CHARACTERISTICS 

Definition. — A  sac-like  investment  of  fibrous  tissue  of  the 
non-erupted  teeth  of  man,  and  many  animals,  which  disappears 
after  histogenetic  periods  have  passed. 

Origin. — From  the  mesodermic  cells  of  the  outer  portion  of 
the  dentinal  papilla. 

Macroscopical  Appearances. — A  rather  tough,  pale  membrane 
easily  stripped  off  the  surface  of  teeth  which  have  not  yet 
arrived  at  the  proper  time  for  eruption.  The  author  has  been 


THE    DENTAL    CAPSULE  213 

unable  to  find  another  organ  in  the  body  which  is  its  counter- 
part. It  exists  for  a  few  years  only,  and  when  its  work — that  of 
protecting  the  crown  of  the  erupting  tooth,  after  being  instru- 
mental in  generating  the  cementum  and  periodontal  membrane 
— is  accomplished,  it  disappears  entirely,  completely  differing 
from  such  organs  as  the  uterine  adnexa,  which  persist  after  the 
cessation  of  their  functions,  and  even  the  thymus  gland,  which, 
as  a  rule,  leaves  traces  behind.  It  can  be  fairly  claimed  for  the 




FIG.   187. — Degeneration   and   vacuolation   of   the   dental   capsule   prior   to   its 

disappearance. 


dental  capsule  that  in  this  respect  it  is  unique.  Regarded  from 
an  embryological  aspect,  the  dental  capsule,  e.g.,  of  the  first 
premolar,  may  be  observed  in  certain  portions  of  the  oral  sub- 
mucous  and  alveolar  tissues  about  the  ninetieth  day  of  intra- 
uterine  life  in  man,  and  can  be  well  demonstrated  in  sagittal 
sections  of  the  jaws  of  kittens  three  weeks  old.  The  cells  are 
very  elongated  and  thin,  with  small  lenticular  nuclei,  chiefly 
arranged  in  longitudinal  bundles  corresponding  to  the  long  axis 
of  the  tooth  germ.  Later  on  they  become  developed  into  the 


214 


THE    ORAL   TISSUES 


extended  fusiform  cells  of  fibrous  connective  tissue.  Eventu- 
ally the  capsule  undergoes  atrophy  and  degeneration  by  the  loss 
of  the  nuclei  of  its  cells  and  vacuolation  of  its  substance,  in  this 
specific  instance,  about  the  seventh  to  the  ninth  year  in  man. 
This  vacuolation,  it  is  important  to  notice,  occurs  as  a  normal 


FIG.  188. — Sagittal  section  in  the  incisor  and  canine  regions  of  mandible  of 
a  young  heifer.  Prepared  by  cutting  through  the  jaw  with  a  saw  while  in  the 
recent  state.  Actual  size.  Shows  (p)  the  permanent  tooth  in  its  (F)  capsule; 
T.  Functional  deciduous  incisor. 


change  in  the  capsules  of  teeth  about  to  erupt,  of  course  just  prior 
to  their  disappearance;  but  when  a  tooth  is  retained  in  situ  in 
the  bone,  it  does  not  follow  that  it  undergoes  this  vacuolation. 


It  is  composed  of  bundles  of  white  connective  tissue  fibres, 
running  in  a  complex  and  varied  fashion  and  interlacing  in  all 
directions.  The  cellular  elements,  as  well  as  the  vascular 


THE    DENTAL    CAPSULE 


215 


supply,  are  scanty.  The  outer  portion  is  less  dense  than  the 
inner,  but  it  cannot  be  removed  as  a  separate  layer  from  the 
latter,  as  neither  is  divided  by  a  pronounced  line  of  demarca- 
tion. The  inner  is  dense,  and  is  covered  on  its  free  surface,  i.e., 
the  part  directed  towards  the  enamel  and  cementum  with  a  flat 
layer  of  epithelial  cells,  which  are  manifestly  part  of  the  layer 
of  polygonal  cells  of  Nasmyth's  membrane. 

Running    inwards    towards    this    cellular    layer    groups    of 
tube-like  epithelial  bodies  wind  between  the  fibres.     They  are 


FIG.  189. — A  tubular  gland-like  structure  from  the  dental  capsule  of  man. 
Prepared  by  "fixing,"  hardening,  and  cutting  on  an  ether- freezing  microtome. 
Stained  with  Ehrlich's  acid  hasmatoxylene.  Magnified  250  times. 


simple  in  construction,  though  sometimes  they  may  branch. 
They  have  no  definite  lumina;  but  the  epithelial  cells  which 
line  the  basement  membrane  are  cubical  in  shape  and  have 
large  prominent  nuclei.  They  end  in  culs-de-sac.  Their 
function  is  unknown,  and  their  origin  doubtful,  although  it 
is  quite  possible  that  they  may  be  derived  originally  from 
''rests"  or  vestigial  remnants  of  the  unatrophied  epithelium  of 
the  tooth-band. 


2l6 


THE    ORAL   TISSUES 


THE    GUM 


MICROSCOPICAL  ELEMENTS: — (i)  Epithelium  of  the  mucous  membrane; 
(ii)  Simple  and  compound  papillae;  (iii)  Mucous  glands;  (iv)!  Fat 
lobules;  (v)  Blood-vessels;  (vi)  "Glands"  of  Serres. 

GENERAL   CHARACTERISTICS 

Definition, — The  soft  dense  tissue  which  clothes  the  alveo- 
lar processes  of  the  jaws,  being  intimately  connected  with  their 
periosteum,  and  surrounding  the  necks  of  the  teeth. 


OE 


FIG.  190. — The  margins  of  the  gingival  tissue  in  an  interdental  space.  Magni- 
fied 200  times.  Stained  with  haematoxylene.  O.K.  Oral  epithelium  of  the  gin- 
gival tissue;  D.  and  c.  Dentine  and  cementum  of  two  contiguous  teeth,  that  on  the 
left  being  hyperplasic. 

Origin. — The  superficial  epithelial  portion  is  derived  from  the 
stomodaeal  ectoderm,  the  submucous  tissue  from  the  stomodaeal 
mesoderm,  both  due  to  the  backward  involution  of  these  parts 
of  the  blastoderm  between  the  maxillary  and  mandibular 
processes  of  the  head. 

This  involution  deepens  and  extends  further  backwards, 
till  a  thin  partition  only  intervenes  between  it  and  the  caecal 
extremity  of  the  fore-gut.  On  the  absorption  of  this,  connec- 
tion with  the  pharyngeal  cavity  is  permanently  established. 


THE    GUM  217 

Macroscopical  Appearances. — The  gum  is  a  smooth,  firm, 
pale  pink  tissue  round  the  necks  of  the  teeth,  continuous 
externally  with  the  sulci  between  the  lips  and  cheeks,  and 
internally  with  the  hard  and  soft  palates,  floor  of  mouth  and 
root  and  sides  of  tongue.  The  gum  envelops  the  arches  of  the 
osseous  septa  between  the  teeth  in  much  the  same  way,  but 
not  to  so  great  an  extent  as  over  the  external  and  alveolar 
plates  (see  Figs.  191  to  194).  In  normal  conditions  there  are 
no  interdental  papillae. 


GT 


OE 


BT 


FIG.  191. — Gingival  tissue  covering  an  interdental  septr  ^  of  bone,  showing 
oral  epithelium,  and  character  of  sub-epithelial  parts.  A.agnified  200  times. 
Stained  with  haematoxylene.  O.K.  Oral  epithelium;  G.T.  Gingival  tissue;  B.T. 
Free  termination  of  alveolar  tJone;  p.  Periosteum. 


HISTOBOGY 

The  minute  anatomy  of  the  gum  may  be  conveniently 
considered  under  the  following  heads:  (A)  The  mucous  mem- 
brane; (B)  The  submucous  tissue. 

A 

The  mucous  membrane,  about  0.3  mm.  thick,  is  essentially 
of  a  stratified  epithelial  character,  consisting  as  it  does  of 


2l8 


THE    ORAL   TISSUES 


G  T 


OEi 


G  T 


FIG.  192. — Another  portion  of  the  gingival  tissues  covering  an  interdental  sep 
turn  of  bone.      Magnified  200  times.     Stained  with  haematoxylene.     O.Ei.  Normal 
oral  epithelium;  O.EZ.  Deeper  and  more  abundant  oral  epithelium;  G.T.  Normal 
gingival  tissue. 


OE 


FIG.  193. — Gingival  tissues  covering  another  interdental  septum  of  bone . 
Magnified  200  times.  Stained  with  hrematoxylene.  o.E.  Thin  layer  of  stratified 
squamous  epithelium;  G.T.  Normal  gingival  tissue. 


THE.  GUM 


2IQ 


FIG.  194. — Vertical   section   of    the    gum.     Prepared    similarly    to    Fig.    193. 
Stained    with    Ehrlich's    acid    hasmatoxylene.      Magnified     50    times.     A.   Oral 
epithelium;  p.  Papilla  of  the  submucous  tissue;  c.  Connective  tissue  fibres  inter- 
lacing in  all  directions;  D.  Scanty  cellular  elements;  v.  Blood-vessel;  T.T.  Parts  o 
the  section  bordering  the  gingival  trough,  torn  in  cutting;  B.  Alveolar  bone. 


22O  THE    ORAL   TISSUES 

several  layers.  On  the  surface  are  large,  stratified,  squamous 
epithelial  cells  which  overlap  each  other  to  some  extent.  Deeper, 
they  become  more  cubical  in  shape,  but  the  deepest  of  all  are 
columnar  in  outline,  and  form  the  rete  Malpighii,  resting  on  an 
exceedingly  thin  basement  membrane.  In  the  lower  layers  the 
shape  of  the  cells  is  modified  by  their  mutual  apposition. 
They  fit  each  other  very  closely.  The  epithelium  of  the  gum 
can  be  divided  into  the  layers  known  as  the  stratum  corneum, 


c 


FIG.  195. — Vertical  section  of  the  oral  epithelium.  Stained  with  Ehrlich's 
acid  haematoxylene.  Magnified  250  times.  O.E.  Epithelium  of  gum  (oldest 
cells);  B.B.  Intercellular  bridges  of  the  "spiny"  cells;  R.  Rete  Malpighii;  c. 
Corium. 

stratum  lucidum,  and  stratum  granulosum,  as  in  the  epidermis, 
and  possibly  there  is  eleiden  or  granular  material  deposited 
in  the  older,  more  superficial  cells. 

The  deeper  cells  are  more  protoplasmic  than  the  others, 
undergo  repeated  karyokinesis,  and  gradually  push  outwards 
the  latter,  which  ultimately  become  lost  by  abrasion. 

Many  "spiny  cells,"  separated  by  systems  of  wide  intercel- 
lular channels,  are  often  noticed  in  the  layers  nearest  to  the 
rete  mucosum  or  Malpighii. 


THE    GUM  221 

This  last  named  consists  of  a  very  folded  line  of  columnar 
cells,  placed  vertically  on  the  surface  of  the  papillae,  which 
are  formed  by  the  submucous  tissue. 

The  epithelial  mucous  membrane  is  perforated  here  and 
there  to  allow  the  passage  of  the  ducts  of  many  mucous  glands, 
which  are  present  in  the  sub-lying  region. 

The  gingival  tiough  extends  to  a  depth  of  2.5  to  4  mm.  in 
different  situations,  and  always  contains,  even  in  the  healthiest 
of  mouths,  microorganisms  of  the  Micrococcus  Catarr kalis,  and 
Streptococcus  pyogenes  groups.  It  is  bounded  internally  by  the 
enamel,  externally  by  the  stratified  squamous  epithelium  of  the 
gingival  tissues. 

B 

The  sub-mucous  tissue  consists  of  dense  bundles  of  connective 
tissue  arranged  throughout  its  substance.  These  are  closely 
associated  with  the  fibres  of  the  alveolar  periosteum,  and  at  the 
necks  of  the  teeth,  with  the  "principal"  fibres  of  the  alveolo- 
dental  periosteum.  They  pass  outwards  in  fan-shaped  fas- 
ciculi to  the  surface  of  the  numerous  papillae. 

The  latter  are  large  elevations  of  the  sub-mucous  fibrous  tissue. 
They  form  the  base  on  which  the  cells  of  the  rete  mucosum  rest, 
and  between  them  are  depressions  which  vary  indefinitely  in 
size  and  shape.  A  simple  papilla  consists  of  one  large  mound  or 
elevation  of  vascular  fibrous  tissue,  the  term  "compound" 
being  applied  to  those  larger  ridges,  which  are  further  sub-di- 
vived  by  smaller  ones  passing  in  from  without.  The  papillae  are 
visible  to  the  naked  eye,  if,  after  removal  of  the  epithelium  by 
means  of  some  dissociating  fluid,  the  free  surface  of  the  gum  be 
examined. 

Among  the  connective  tissue  fibres  plasma  cells  are  frequently 
seen.  These  are  large  cells  with  round,  eccentrically  placed 
nuclei  whose  chromatin  stains  intensely.  Their  cytoplasm  is 
dense  and  stains  deeply.  Occasionally  they  contain  vacuoles, 
which  when  filled  with  semi-fluid  substances  are  recognised  as 
Russell's  fuchsine  bodies.  Mast  cells  and  leucocytes  are  often, 
also,  found. 


222  THE    ORAL   TISSUES 

Other  constituents  of  the  sub-epithelial  tissue  are : — 
(i)  Small  lobules  of  fat  cells — tiny  oval  vesicles  (each  cell 
being  about  yoju  in  diameter) — of  adipose  material  gathered 
together  into  clusters,  and  imbedded  in  a  fine  reticulum  of 
areolar  connective  tissue;  (ii)  Mucous  glands,  similar  to  those 
described  on  page  189;  (iii)  Blood-vessels,  which  are  abun- 
dantly distributed;  (iv)  Scanty  nerve  fasciculi;  and  (v)  the  so- 
called  "glands"  of  Serres. 


MG 


FIG.  196. — Gingival  tissue  covering  the  internal  alveolar  plate  of  the  incisor 
region  of  a  woman  of  25  years.  Normal.  Magnified  200  times.  Stained  with 
hsematoxylene  and  cosine.  O.E.  Stratified  squamous  epithelium;  A.B.  Bone  of  the 
internal  alveolar  plate;  M.G.  Mucous  gland;  D.  Duct  of  mucous  gland. 

There  are  large  mucous  glands  in  the  gum  at  the  cervical 
margins  of  the  teeth  on  the  lingual  or  palatal  side,  none  in  that 
on  the  labio-buccal  aspect  of  the  alveolar  process.  The  author 
experimentally  proved  this  by  excising  a  portion  of  normal  gum 
immediately  in  contact  with  the  teeth,  on  the  outer  side  of  the 
alveolar  process  of  the  mandible  of  a  man,  aged  about  forty- 
four,  and  chose  a  spot  between  the  two  right  premolars.  It 
measured  6.5  mm.  in  length.  There  was  no  mucous  gland 
to  be  seen.  Similarly  none  was  present  in  the  gum  on  the  labial 
aspect  of  the  bone  over  the  root  of  the  second  left  maxillary 


THE   MAXILLARY   SINUS  223 

incisor  of  a  woman  aged  twenty-five.  Again,  in  a  piece  of  the 
tissue,  over  the  septum  which  intervenes  between  two  man- 
dibular  molars,  no  mucous  gland  was  found.  The  reason  is 
obvious.  Mucous  glands  are  not  wanted  in  the  former  situa- 
tion, because  of  the  existence  of  countless  numbers  which  open 
on  the  free  surfaces  of  the  lips  and  cheeks  and  in  the  latter 
situation  because  of  lack  of  room. 

The  "glands"  of  Serres  (see  Figs.  251  and  253),  according  to 
Tomes  (op.  cit.  p.  126),  are  "  small  round  aggregations  of  pave- 
ment epithelium,  met  with  at  a  little  depth,  or  even  imbedded 
in  the  surface."  These  have  no  known  function,  but  are  rem- 
nants of  the  dental  lamina  or  tooth-band.  Bland-Sutton  and 
R.  R.  Andrews1  consider  them  to  be  histologically  comparable 
to  young  enamel  organs;  but  Sayre  Marshall2  erroneously 
describes  them  as  lobulated  glandular  structures. 

THE  MUCOSA  OF  THE  ANTRUM  OF  HIGHMORE 

MICROSCOPICAL    ELEMENTS:— (i)    Epithelium;    (ii)    Submucous    Tissue; 
(iii)  Glands. 

GENERAL   CHARACTERISTICS 

The  histology  of  this  tissue  seems  to  have  escaped  the  notice 
of  workers,  who,  generally  speaking,  have  contented  themselves 
by  saying  that  it  is  continuous  with,  and  similar  to  the  Schnei- 
derian  mucous  membrane  of  the  nose. 

A  knowledge  of  its  minute  structure  is  important  because  of 
its  intimacy  with  the  roots  of  the  first  and  second  maxillary 
molars,  or  premolars,  and  the  fact  that  treatment  of  its  diseased 
conditions  not  infrequently  comes  into  the  province  of  the  work 
of  the  dental  surgeon. 

Regarding  its  anatomy,  Sappey3  describes  it  as  being  supplied 

1  "American  Text-Book  of  Operative  Dentistry,''  p.  90,  1901. 

2  "Principles  and  Practices  of  Operative  Dentistry,"  p.  58,  1901. 

3  "Quant  au  sinus  maxillaire,  elles  (the  glands)  repandent  sur  tous  les  points 
de  ses  parois  avec  une  telle  profusion,  qu'il  serait  fort  difficile  d'en  faire  le 
denombrement.  .  .  .  Ces  glandes  affectent,  du  reste,  toutes  les  dimensions  et 
toutes  les  formes  possibles:  il  y  en  a  de  tres  considerables  et  de  tres  compliques, 
de  moyennes,  et  plus  simples,  de  petites,  de  tres  minimes,  et  enfin  d'uni-utricular. 
Les  unes  revetent  la  forme  arrondie,  d'autres  la  forme  rameuse,  d'autres  les 
formes  intermediares.  Elles  sont  surtout  remarquables  par  la  dilatation 
extrement  frequente  de  leur  conduit,  en  sorte  que  sur  un  grande  nombre,  d'entre 
elles  il  existe  un  kyste,  naissant,  ou  ayant  deja  acquis  une  certain  development  ou 
completement  developpe." — "Traite  d'Anatomie,''  Vol.  III.,  Paris,  p.  660,  1871. 


224  THE    ORAL   TISSUES 

with  glands,  which,  in  appearance,  are  much  like  the  Meibo- 
mian  glands  of  the  eyelids.  They  are  irregularly  distributed, 
and  much  scantier  than  those  of  other  mucous  membranes. 

Definition. — The  lining  membrane  of  the  maxillary  sinus, 
otherwise  called  the  antrum  of  Highmore. 

Origin. — It  is  an  outward  involution  of  the  ectoderm  of  the 
olfactory  fossae,  which  themselves  originate  at  a  point  below 
and  in  front  of  the  ocular  vesicle.  It  is  said  that  it  begins  to 
develope  about  the  fourth  month  of  intra-uterine  life. 

Macroscopical  Appearances. — A  thin  whitish  tough  mem- 
brane, very  readily  removed  from  the  bone,  and  in  places 
thrown  into  slight  rugae.  In  old  subjects  (cet.  64)  patches  of 
pinkish  material  (inspissated  mucus)  may  be  seen.  The  thin- 
ness is  not  uniform,  in  health,  large  territories  may  be  found 
somewhat  thicker  than  the  rest.  It  is  also  slightly  thicker  over 
the  situations  of  the  glands. 

It  measures  0.7  mm.  to  0.9  mm.  in  thickness.  The  whiteness 
is  due  to  lack  of  blood  supply,  which  is  particularly  scanty.  The 
vessels  come  from  the  anterior  and  posterior  ethmoidal  branches 
of  the  orbital  group  of  the  ophthalmic  artery.  Bodecker,  in  this 
connection,  says  (op.  cit.}  "The  blood-vessels  are  principally 
derived  from  the  mucous  membrane  of  the  nasal  cavity, 
although  some  of  the  smaller  branches  arise  from  the  posterior 
dental  arteries  through  the  alveoli." 

Its  toughness  depends  upon  the  large  amount  of  white  con- 
nective tissue  fibres  which  go  to  make  up  the  greater  proportion 
of  its  bulk.  Sections  curl  up  very  readily,  and  large  pieces  can 
be  torn  off  the  thin  bony  walls  to  which  it  is  but  loosely  attached 
by  fibrous  tissue. 

HISTOLOGY 

The  lining  membrane  presents  for  microscopical  examina- 
tion— (i)  An  epithelial  surface,  (ii)  sub-epithelial  tissue,  (iii) 
certain  glandular  structures,  and  (iv)  its  periosteal  attachment. 

(i)  The  Surface  Epithelium 

In  common  with  the  mucous  membrane  of  the  respiratory 
passages  (except  that  of  the  olfactory  region  of  the  nose),  the 


THE    MAXILLARY   SINUS  225 

upper  surface  of  the  soft  palate,  the  nasal  region  of  the  pharynx, 
and  several  other  organs  of  the  body,  the  epithelium  of  the 
antral  mucosa  consists  of  a  transitional  layer  of  ciliated  co- 
lumnar epithelial  cells,  situated  side  by  side,  and  on  and  between 
several  layers  of  variously  shaped  cells,  the  lowest  stratum  of 
which  is  placed  on  a  delicate  basement  membrane.  This  cov- 
ers the  whole  of  the  mucous  membrane. 

The  layer  of  epithelium  measures  about  0.02  mm.  in  depth  in 
young  subjects  (at.  25). 

Each  superficial  cell  is  granular,  narrow,  more  or  less  colum- 
nar in  shape,  and  bears,  at  its  free  end,  a  number  of  long  cilia, 
which  are  securely  fixed  to  the  surface  of  a  clear  disc.  The 
attached  basal  extremity  of  the  cell  is  generally  pointed  or 
dichotomous. 

The  intervening  and  deep-lying  cells  are  pyriform  or  polyhe- 
dral, thus  called,  by  some  authors,  "battledore  cells,"  whilst 
the  deepest  cells  are  spherical.  All  have  very  pronounced  oval 
nuclei,  which  in  the  case  of  the  first-named  is  situated  near 
the  refractile  disc. 

Some  authors  consider  that  the  younger  spherical  cells  finally 
replace  those  possessing  cilia;  but  probably  this  is  not  true,  as 
they  appear  to  contain  mucigen,  and  to  become  ultimately 
distended  into  the  shape  of  goblet-cells. 

At  intervals  numerous  goblet  or  chalice  cells  may  be  observed 
between  their  ciliated  neighbours. 

These  are  large  poculiform  bodies,  with  wide  open  mouths, 
which  are  directed  inwards  towards  the  centre  of  the  antrum. 
Each  contains  mucigen  and  an  indistinct  small  nucleus  placed 
•at  its  distal  end.  The  mucus  may  entirely  or  only  partially 
fill  it;  but  sometimes  it  can  be  observed  in  sections,  becoming 
extruded  from  the  mouth  of  the  cell. 

(ii}  The  Sub-Epithelial  Tissue 

is  very  loose,  and  sparsely  supplied  with  cells  and  blood-vessels, 
though  glands  are  fairly  abundant.  It  is  made  up  of  bundles 
x)f  white  connective  tissues  fibres,  \vhich,  while  in  no  sense 
compactly  arranged,  are  still  very  tough.  The  author  has 

IS 


226 


THE    ORAL   TISSUES 


never  noticed  the  presence  of  any  elastic  tissue  fibres  in  this 
membrane. 

(Hi)  The  Glands 

are  of  great  interest.  They  are  visible  macroscopically  in 
suitably  stained  specimens,  as  pin-point  spots  more  deeply 
coloured  than  the  rest  of  the  tissue.  Seen  in  sections  cut  in  a 


FIG.  197. — A  mucous  gland  of  the  lining  membrane  of  the  antrum  of  High- 
more.  Stained  with  Ehrlich's  acid  haematoxylene,  counter-stained  with  cosine. 
Magnified  250  times.  A.  Mucous  secreting  cells  in  activity;  R.  The  same  after 
the  period  of  activity  is  passed;  c.  Crescent  of  Gianuzzi. 

plane  perpendicular  to  the  surface  of  the  bone  of  the  antrum, 
they  present  the  appearance  of  tubular  glands;  and  this,  no 
doubt,  led  Sappey  to  assert  that  they  resemble  the  Meibomian 
glands  in  the  eyelids.  Such,  however,  is  not  the  case,  for  if 
sections  be  made  in  an  oblique  direction,  or  in  a  plane  parallel 
with  the  surface  of  the  antral  bone,  below  the  level  of  the 
epithelial  layers,  they  are  at  once  recognised  as  compound 
racemose  bodies,  consisting  of  well-defined  lobules,  and  having 
single  ducts,  which  open  on  to  the  free  surface  of  the  mucous 
membrane. 


THE    MAXILLARY    SINUS  227 

The  largest  glands  measure  in  length  0.8  mm.  to  1.3  mm., 
and  0.2  mm.  to  0.6  mm.  in  depth.  The  lobules  assume  varying 
shapes  (see  Fig.  197),  and  are  held  together  by  delicate  strands 
of  connective  tissue.  Each  lobule  possesses  a  small  duct,  which 
communicates  with  a  larger  excretory  duct,  and  its  constituent 
parts  are  composed  of  a  number  of  alveoli  or  acini.  Glands 
during  rest,  and  after  a  period  of  activity,  are  clearly  observed. 

These  latter  consist  of  a  basement  membrane,  on  which 
rest,  by  means  of  their  broad  bases,  five  or  six,  or  more,  large 
polygonal  secretory  cells.  Others  often  fill  the  acini,  leaving 
but  little  room  for  lumina.  Their  translucent  interiors  are 
traversed  [by  an  exceedingly  minute  reticulum  [of  fibrils, 


PlG.   198. — Diagram  of  Fig.  197  shows  the  secreting  mucous  cells  about  to  begin 
their  functions.     Several  crescents  of  Gianuzzi  can  be  seen. 


which  includes  in  its  meshes  mucigen,  small  indifferent  flattened 
nuclei  being  placed  at  the  periphery  of  each  cell.  The  crescents 
or  lunulas  of  Gianuzzi — groups  of  small  crescentic  granular 
nucleated  bodies — may  be  found  occasionally  in  places  between 
the  bases  of  the  cells,  more  darkly  stained  than  the  other  parts 
of  the  acini. 

The  ducts  are  short,  straight  tubes,  of  about  0.02  mm.  in 
length.  In  width  at  their  orifices  they  may  measure  as  much 
as  i  mm.  At  their  junctions  with  the  gland  substance  proper 
their  diameters  are  less,  as  they  are  somewhat  truncated. 
They  are  lined  with  a  simple  layer  of  small  cubical  epithelial 
cells. 

(iv)  The  Periosteal  Attachment 

is  due  to  the  presence  of  strong  bands  of  connective  tissue  which 
pass  into  the  peripheric  laminae  of  the  bone. 


PART  III 


CHAPTER  XII 
THE  DEVELOPMENT  OF  THE  TEETH  IN  MAMMALIA 

MICROSCOPICAL  ELEMENTS  IN: — (i)  The  Enamel  Organ;  (ii)  Dentine  Germ; 
(iii)  Dental  Capsule,  (iv)  During  later  periods  of  the  formation  and 
growth  of  the  enamel,  dentine,  and  cementum;  and  (v)  Appear- 
ances in  human  embryos  at  half  term. 

For  purposes  of  description  it  will  be  convenient  to  divide 
the  series  of  phenomena  which  take  place  during  the  histo- 
genesis  of  the  deciduous  and  permanent  teeth  and  surrounding 
structures,  into: 

(A)  The  changes  occurring  in  the  jaws  before  and  up  to 
the  period  of  formation  of  the  dentine  germ, 

(B)  The  metamorphoses  occurring  in  and  around  the  tooth 
germ  at  the  period  of  formation  of  the  dentine  germ, 

(C)  Subsequent  stages  of  development. 


Earliest  Phases  of  Evolution 

At  a  very  early  period  of  intra-uterine  life  in  man,  viz., 
about  the  4oth  to  45th  day,  the  embryo  measuring  about  12  cm. 
in  length,  the  first  signs  of  change  are  noticeable.  The  date 
synchronises  with  the  commencement  of  ossification  of  the 
clavicle,  the  first  of  all  bones  to  ossify. 

(i)  Changes  in  the  Ectoderm 

Coronal  sections  through  the  anterior  part  of  the  embryonic 
head  before  this  age  show  that  there  is  a  slight  appreciable 
thickening  of  the  stomodaeal  ectoderm  over  the  regions  of  the 

231 


232 


DENTAL   HISTOGENESIS 


embryonic  alveolar  processes,  that  is,  the  promontories  of 
tissue  known  as  the  maxillary  processes  of  the  embryonic  face, 
which,  having  met  the  lateral  plates  of  the  fronto-nasal  proc- 
ess, have  continued  their  growth  downwards  and  inwards, 
and  joined  the  mid-frontal  process  to  complete  the  alveolar 
arch  and  maxillary  bone.  In  the  mandibular  arch  the  changes 
begin  above  the  cartilage  of  Meckel,  and  at  places  a  little 
external  to  the  primitive  elevation  of  the  tongue. 

M  FP 


M  P 


FIG.  199. — Coronal  section  through  head  of  a  human  embryo,  exact  age  un- 
known. Prepared  as  other  soft  tissues.  Stained  en  masse  with  borax-carmine, 
and  cut  in  paraffin  wax.  Magnified  20  times.  To  show  the  development  of 
the  maxills.  M.P.  Maxillary  process;  M.F.P.  Mid-frontal  process;  L.P.  Lateral 
plates  of  fronto-nasal  process. 

The  contour  of  the  rete  Malpighii  is  undisturbed  in  its  clear 
outline  and  flattened  appearance. 

The  epithelial  surface  of  the  mouth  is  extremely  thin  and 
undeveloped,  consisting  of  a  few  flat  cells,  while  the  rete  Mal- 
pighii is  almost  indistinguishable  from  the  rest  of  the  ectoderm. 
A  great  depth  in  the  mucosa  is  noticed,  and  the  bones  which 
will  ultimately  form  the  crypts  of  the  teeth  are  beginning  to 
appear  and  stain  deeply. 


DEVELOPMENT  OF  TEETH  IN  Mammalia 


233 


In  the  kitten,  the  start  in  the  development  of  the  bony 
alveoli  is  delayed  at  this  time,  and  even  later;  but  in  man, 
the  osseous  framework  begins  to  assume  a  somewhat  different 
shape,  and  is  a  prominent  feature  in  specimens  of  an  earlier 
date  than  the  4oth  day. 

At  this  age,  however,  a  marked  metamorphosis  in  the 
ectoderm  can  be  observed. 


TG 


TO 


TG 


FIG.  200. — Coronal  section  through  head  of  embryo  of  cat.  Prepared  and 
stained  as  last  figure.  Magnified  20  times.  Represents  the  stage  of  develop- 
ment in  man  at  about  the  5Oth  day  of  intra-uterine  life.  T.G.  Tooth  germ; 
Z.  Tooth  band;  L.F.  Lip-furrow;  T.  Tongue;  M.  Meckel's  cartilage;  B.  Commence- 
ment of  formation  of  bone  of  alveolus. 

(ii)  Formation  of  the  Dental  Furrow 

Its  free  surface  appears  to  be  slightly  indented  (''The  primi- 
tive dental  furrow"),  in  most  cases,  and  follows  fairly  closely 
the  lines  of  contour  of  the  rete  Malpighii.  Over  the  palate 
in  places,  it  is  one  cell  thick,  but  over  the  floor  of  the  buccal 
cavity,-  as  well  as  its  sides,  and  the  sides  of  the  roof,  four, 
five,  eight,  or  even  nine  rows  of  cubical  or  polygonal  cells 
can  be  counted.  The  large  size  of  their  oval  nuclei  arrests 
attention.  The  cubical  cells  are  set  on  what  looks  like  a 


234  DENTAL   HISTOGENESIS 

delicate  line  or  basement  membrane.  A  few  small  flat  squa- 
mous  cells  are  often  found  here  and  there,  coherent  to  the 
surface  epithelium. 

As  the  epithelium  approaches  the  place  where  the  primary 
inflection  is  about  to  occur,  it  becomes  thickened.1  The  nuclei 
become  considerably  elongated,  and  almost  fill  the  cells  which 
themselves  have  undergone  some  amount  of  lengthening. 

The  epithelial  surface  is  clearly  distinguishable  from  the 
underlying  tissues,  for  two  reasons: — It  takes  the  stain  more 
intensely,  and  its  cellular  constituents  are  crowded  together. 
In  other  words,  its  appearance  is  identical  with  that  which 
is  about  to  form  the  Schneiderian  membrane  of  the  nose,  the 
surface  epithelium  of  the  skin  of  the  face,  and  the  under  surface 
of  the  tongue. 

The  ectoderm  would  appear  to  be  formed  some  considerable 
time  after  the  mesoderm,  that  is,  it  is  an  involution  of  the 
superficial  layer  of  the  blastoderm  reflected  backwards  into 
the  mesoderm.  Its  genesis  is  probably  synchronous  with  that 
of  the  nasal  fossae,  external  skin,  and  mucous  membrane  of 
the  cheeks. 

(iii)  The  Primary  Epithelial  Inflection 

In  coronal  sections  of  the  maxillae  the  first  epithelial  in- 
volution into  the  subjacent  mesoderm  begins  at  a  spot  a  little 
external  to  the  lateral  margins  of  the  tongue,  in  the  mandible 
some  distance  internal  to  those  margins.  The  invagination 
extends  right  round  the  jaws,  and  thus  forms  a  continuous 
semi-circular  band  of  cells  enclosed  by  mesodermic  tissue. 
In  vertical  sections  it  looks  like  a  narrow  finger-like  penetra- 
tion of  cells  into  the  mesoderm:  in  side  section  it  is  seen  to 
be  a  continuous  flat  band  extending  from  the  surface  into  the 
jaw. 

(i)  Origin  of  the  Lip-furrow  and  Tooth  Band 

At  the  4o-45th  day  a  splitting  of  this  primary  inflection 
occurs,  not  across,  but  in  a  longitudinal  direction  with  it;  thus 

1  This  epithelial  thickening  is  greatest  along  the  line  of  the  future  jaw  on  the 
surface  of  which  it  extends  longitudinally,  and  is  produced  by  sub-division  and 
repeated  multiplication  of  the  deepest  cells. 


DEVELOPMENT  OF  TEETH  IN  Mammalia  235 

it  becomes  divided  into  two  parts,  an  outer  and  an  inner. 
The  former  is  towards  what  will  be  the  labial  side,  the  latter 
towards  the  tongue.  The  former,  known  as  the  labio-dental 
strand,  or  lip-furrow,  passes  in  a  perpendicular  direction, 
and  ultimately  produces  the  groove  which  is  afterwards  the 
furrow  between  the  lips  and  the  alveolar  processes  of  the  jaws : 
while  the  latter,  known  as  the  common  dental  germ,  or  tooth 
band,  is  penetrating  the  mesoderm  in  a  horizontal  direction, 
and  becomes  the  layer  of  cells,  in  connection  with  which  both 
the  deciduous  and  permanent  teeth  are  developed. 

EI 


L  F- 


FIG.  201. — Diagram  to  show  method  qf  cleavage  of  the  primary  epithelial 
inflection.  E.L.  Ingrowth  of  epithelium;  L.F.  Lip-furrow  on  outer  or  buccal  side; 
z.  Tooth  band  on  lingual  side;  F.  Free  growing  end  whence  the  permanent  tooth 
germs  will  arise. 

The  opposing  theories  regarding  the  relations  to  each  other 
of  lip  furrow  and  tooth  band  may  be,  here,  briefly  noted. 
Thus: 

(i)  Rose1  affirms  that  both  have  a  common  origin,  as  just 

described. 

(ii)  Baume2  believes  that  the  tooth  band  arises  from  the 
side  of,  or  is  merely  a  process  of  the  lip  furrow,  an 
opinion  shared  also  by 

(iii)  Xavier    Sudduth,3    who    says: — "The   lamina   is   only 

an"  offshoot  from  the  side  of  the  band,  which  becomes 

somewhat  shallower,  and  in  some  instances  disappears." 

(iv)  Leche4  holds  that  both  are  developed  separately,  but 

simultaneously. 

1  "  Archiv.  f.  mikros.  Anatomic."     Bd  xxxviii,  1891,  and  "  Anat.  Anzeig,"  1896. 
2"Versuch   einer   Entwickelungsgeschichte   des   gebisses,"  in  Odontologische 
Forschungen,  1882. 

3  "American  System  of  Dentistry,"  p.  620,  1887. 

4"Morph.  Jahrbuch,  "  1892,  and  "Bibliotheca  Zoologka,"  1895. 


236 


DENTAL  HISTOGENESIS 


At  this  time  the  tooth  band  possesses  an  attached  edge  or 
border,  which  is  continuous  with  the  surface  epithelial  cells, 
and  a  free  edge  or  border,  which  penetrates  more  deeply  inwards. 
It  is  from  this  free  edge  that  the  ten  deciduous  tooth  germs 
in  each  jaw  will  be  developed. 

Still  examining  the  coronal  sections  through  the  embryonic 
head,  it  is  seen  that  each  tooth  germ  is  accurately  directed 


OE 


LF 


FIG.  202. — Diagram  of  a  sagittal  section  through  the  germ  of  the  first  man- 
dibular  milk  molar  of  a  human  embryo  30  mm.  long.  O.E.  Oral  epithelium; 
L.F.  Lip-furrow;  z.  Tooth  band;  p.  Site  of  future  dentine  germ  (After  Rdse.) 


OE 


FL  P 

FIG.  203. — Diagram  of  a  similar  section  to  the  preceding  figure,  but  through 
the  germ  of  the  canine  tooth  of  an  embryo  40  mm.  long.  The  lettering  as  in  Fig. 
202.  (After  Rose.) 

towards  the  central  portions  of  the  developing  alveolar  bone: 
thus  the  direction  of  growth  in  the  maxilla  is  upwards  and 
slightly  inwards,  that  in  the  mandible  is  downwards  and  slightly 
inwards.  (See  Figs.  200  and  204.) 

The  cells  lining  the  tooth  band  possess  the  same  histological 
characteristics  as  those  at  its  immediate  junction  with  the 
free  stomodaeal  epithelium;  viz.,  long,  cylindrical  cells  with 
large  oval  granular  nuclei  situated  rather  more  towards  the 
distal  than  the  basal  end. 

They  are  placed  side  by  side  in  a  single  layer,  the  substance 
of  the  tooth  band  being  composed  of  round  or  polygonal  less 
distinct  cells  having  circular,  less  granular  nuclei. 


DEVELOPMENT  OF  TEETH  IN  Mammalia 

z 


237 


OE 


L  F 


FIG.  204. — Coronal  section  of  the  mandible  of  an  embryonic  pig.  Stained 
with  hsematoxylene.  Magnified  45  times.  Represents  the  stage  of  development 
in  man  at  about  the  soth  day.  z.  Tooth  band;  L.F.  Lip-furrow;  O.E.  Epithelium 
of  mouth;  M.  Meckel's  cartilage;  B.  Bone  of  alveolus. 


OE 


E  O 


FIG.  205. — Further  stage  of  growth.  Magnified  45  times.  The  tooth  germ 
in  the  centre  of  the  field  represents  the  stage  of  development  in  man  at  about 
the  6oth  day.  E.G.  First  evolution  of  enamel  "  bud."  Lettering  as  in  preceding 
photomicrograph. 


238  DENTAL   HISTOGENKSIS 

(v)  Changes  in  the  Mesoderm 

Coincidentally  with  these  alterations  of  the  epithelial  sur- 
face, many,  not  all,  of  the  cells  of  the  mesoderm  (hitherto  dis- 
crete) in  the  immediate  proximity  of  the  growing  extremity 
of  each  germ  undergo  three  distinct  and  remarkable  changes. 
First  they  lose  their  identity  as  spherical  mesodermic  cells  with 
rounded  nuclei;  they  undergo  a  fresh  arrangement  of  position; 
they  become  multiplied  in  numbers.  No  longer  do  all  the 
mesodermic  cells  share  like  features  regarding  shape,  the  new 
change  being  that  many  become  elongated,  and  therefore 
spindle-shaped  and  have  fusiform  nuclei.  Those  nearest  the 
rete  Malpighii  of  the  tooth  germ  retain  for  some  time  longer 
their  rounded  outlines.  Their  new  position  is  one  in  which 
their  long  axes  take  up  the  same  direction  as  that  of  the  up- 
growing  tooth  germ.  Their  numbers  are  trebled  or  quadrupled. 
It  must  not  be  forgotten,  however,  that  these  phenomena  are 
only  to  be  observed  at  the  developing  end  of  the  epithelial 
germs. 

(vi)  Evolution  of  the  Enamel  Organ 

The  next  step  in  development  is  concerned  with  the  deepen- 
ing of  the  tooth  band  and  its  lateral  expansion  near,  but  not 
at,  its  free  end,  into  a  bell-like  structure.  This  takes  place  at 
its  deepest  portion,  and  on  its  labial  side.  At  the  superficial 
part  a  slight  constriction  begins  to  take  place;  and  at  about 
the  6oth  or  yoth  day  in  man,  the  first  rudiments  of  the  enamel 
organs  of  the  deciduous  teeth  in  the  incisor  region  can  be  clearly 
discerned.  They  are  called  "  enamel  buds." 

At  certain  spots,  ten  in  number  in  either  jaw,  and  separated 
at  equal  intervals  along  the  continuous  tooth-band  these  cam- 
panular  bodies  are  found.  The  intervening  portion  of  the 
tooth  band  in  its  anterior  part  presently  atrophies  and  finally 
disappears  after  the  lamina  has  become  cribriform,1  while  it 

1  Unatrophied  portions  of  the  tooth  band  frequently  persist.  According  to 
their  growth  they  may  develop  into  elongated  epithelial  masses  in  the  dental 
capsule,  "glands"  of  Serres,  supernumerary  teeth,  enamel  nodules,  accessary 
cusps,  true  geminated  teeth,  or  epithelial  odontomes. 


DEVELOPMENT  or  TEETH  IN  Mammalia 


239 


still  remains  continuous  in  the  posterior  or  molar  region.  The 
primitive  enamel  organs  become  now  specially  organised  and 
constituted. 

Thus  originate  the  earliest  aspects  of  the  enamel  organ.  In 
shape  such  an  organ  is  primarily  like  a  Florence  flask  or  labora- 
tory beaker,  having  a  broad  flattened  concave  base,  and  long 
narrow  neck  opening  on  to  the  free  surface  of  the  epithelium 


o  E 


D  P 


FIG.  206. — Further  stage  of  development.  Magnified  45  times.  Represents 
the  stage  of  development  in  man  at  about  the  yoth  day.  D.P.  Rudiments  of 
dentine  papilla.  Lettering  as  before. 


of  the  mouth.  At  first  the  outline  of  the  enamel  organ  is 
smooth,  but  later  on,  the  external  part  will  become  rather 
sinuous,-  due  to  several  "tufts"  or  "papillary  projections" 
from  the  subjacent  tissue  indenting  the  external  epithelial 
layer  of  cells.  Sometimes  the  tooth  bands  and  the  necks  of 
the  enamel  organs  also  exhibit  these  as  collections  of  polyhedral 
cells  similar  to  those  just  mentioned  (see  Fig.  232).  Capillaries 
from  the  dental  capsule  are  freely  distributed  to  these  "tufts." 
.  In  structure,  the  external  cells  still  assume  a  cylindrical 
character;  the  deepest  are  more  pronounced  than  those  else- 


240 


DENTAL   HISTOGENESIS 


where,  and  they  are  still  continuous  with  the  oral  rete  Malpighii. 
The  interior  is  rilled  with  round  cells,  which  however  speedily 
develop  long  branched  extremities,  and  exhibit,  in  a  rudi- 
mentary fashion,  the  cells  of  the  stellate  reticulum.  It  is  not 
yet  determined  how  these  internal  cells  become  branched,  of 
exactly  in  what  way  the  stellate  reticulum  is  formed.  Some 
observers,  including  Tomes,  have  thought  that,  they  represent 
cells  undergoing  retrogressive  changes — conditions  which  point 


OE 


PIG.  207. — Campanular  form  of  tooth  germ,  from  the  jaw  of  an  embryonic 
kitten.  Stained  with  hasmatoxylene.  Magnified  45  times.  Represents  the 
stage  of  development  in  man  at  ?oth  day.  Lettering  as  before. 

to  their  ultimate  disintegration  and  atrophy;1  butLeon  Williams 
holds  that  they  merely  represent  a  sort  of  intercellular  stroma. 
It  is  nevertheless  certain  that  lengthy  'marked'  branching  proc- 
esses unite  them  together,  their  nuclei,  in  early  stages  of 
growth,  being  in  no  degree  diminished  in  size,  shape,  or  position. 
All  the  central  cells  do  not  become  changed  into  stellate 
bodies.  Certain  numbers,  close  to  the  deepest  layer  of  the 

1  Cf.  The  degenerating  cells  in  the  cysts  of  epithelial  odontomes,  described 
^Chapter  XV,  Vol.  II. 


DEVELOPMENT  OF  TEETH  IN  Mammalia  241 

external  epithelium,  still  retain  their  rotundity,  and  are  ulti- 
mately the  cells  of  the  stratum  intermedium  which  will  presently 
assume  their  completed  shape,  viz.,  that  of  small  polygonal 
rather  branched  cells,  having  connections  externally  with  the 
stellate  reticulum,  and  internally  with  the  internal  epithelium. 

Rapid  growth  now  occurs  at  the  margins  of  each  organ, 
and  the  whole  structure  resembles  a  bell  with  a  handle. 

The  nearest  mesoderm  cells,  about  this  time  (yoth  day  in 
man)  begin  to  proliferate  and  to  be  more  closely  approxi- 

z  w 


FIG.  208. — Diagram  of  a  section  through  the  germ  of  the  first  milk  molar 
of  a  cow's  foetus,  47  mm.  long.  z.\v.  Heaped-up  epithelium  characteristic  of 
ruminants;  E.P.  Enamel  organ;  p.  Site  of  future  dentine  germ.  (After  Rose.) 


mated,  and  eight  primitive  dentine  germs  are  noticed  in  the 
concavities  of  the  enamel  organs. 

The  alveolar  crypts  of  the  anterior  parts  have  become  in- 
creased in  depth  and  importance,  and  begin  now  to  assume  a 
definite  poculiform  shape. 

B 

The  Metamorphoses  Occurring  in  and  around  the  Tooth  Germ  at 
the  Period  of  Formation  of  the  Dentine  Germ 

The  elongation  of  the  necks  of  the  enamel  organs,  the  trans- 
parency of  its  central  portions,  the  density  of  the  dentine 
papilla,  and  the  first  attempts  in  the  formation  of  a  capsule 
or  follicle  or  investing  connective  tissue  sheath,  are  now  ob- 
served (about  looth  day). 

16 


242 


DENTAL   HISTOGENESIS 


While  the  neck  of  the  enamel  organ  extends  more  deeply 
than  ever  into  the  jaw,  it  becomes  still  further  constricted, 


S  M 


D  P 


FIG.  209. — Structure  of  enamel  organ.  From  jaw  of  a  newly  born  kitten. 
Stained  with  borax-carmine.  Magnified  300  times,  o.  Odontoblasts;  D. 
Dentine;  A.  Ameloblasts;  s.M.  Stratum  intermedium;  s.R.  Stellate  reticulum; 
E.E.  External  epithelium ;D. P.  Dentine  papilla;  D.C.  Rudimentary  dental  capsule; 
A.L.  Bone  of  alveolus. 

and  practically  occluded  by  the  apposition  of  opposite  rows  of 
cells. 


DEVELOPMENT  OF  TEETH  IN  Mammalia 


FIG.  210. — Section  of  incisor  of  a  rat.  Magnified  80  times.  A.  Capillary 
loops  torn  out  of  the  secreting  papilla?;  B.  Secreting  papillae  after  removal  of 
capillary  loops;  c.  Ameloblasts;  E.  Enamel;  D.  Dentine.  (Photomicrograph  by 
Leon  Williams.) 


FIG.  211. — Secreting  papillae  and  ameloblasts  from  enamel  organ  of  rat. 
Magnified  600  times.  A.  Papilla  showing  secreting  cells;  B.  Showing  roots  of 
ameloblasts  passing  into  papilla;  c.  Ameloblasts  containing  oval  nuclei;  D. 
Plasmic"  strings  and  granules  emerging  from  ameloblasts.  (Photomicrograph  by 
Leon  Williams.) 


244 


DENTAL   HISTOGENESIS 


The  stellate  reticulum  is  now  near  its  fullest  height  of 
development. 

(vii)  Structure  of  the  Enamel  Organ 

The  periphery  of  the  enamel  organ,  starting  at  the  neck 
(at  one  side)  consists  of  several  rows  of  cubical  or  cylindrical 
epithelial  cells,  whose  oval  nuclei  almost  fill  the  whole  cell. 
At  this  spot  the  most  external  stellate  reticulum  cells  are  flat- 


OE 


EO 


D  P 

FIG.  212. — Later  phase  of  development.  Jaw  of  kitten.  Stained  with 
carmine.  Magnified  65  times.  Represents  the  stage  of  development  in  man  at 
the  85th  day.  z.  Tooth  band  of  permanent  germ;  E.G.  Enamel  organ;  D.P.  Dentine 
papilla  of  deciduous  tooth;  D.  Earliest  trace  of  formation  of  dentine;  O.E.  Oral 
epithelium. 

tened  and  fusiform,  and  probably  represent  immature  stellate 
cells,  but  their  transition  to  the  normal  shape  is  sudden  and 
pronounced. 

At  the  deepest  part  of  the  enamel  organ  many  ovally  nu- 
cleated cylindrical  cells  are  seen,  several  layers  thick.  Passing 
over  the  convexity  of  the  dentine  germ  they  become  aggregated 
more  closely  till,  as  a  palisading,  they  are  most  elongated 
directly  over  the  summit  of  the  convexity.  Above  these  cells 


DEVELOPMENT  OF  TEETH  IN  Mammalia  245 

of  the  internal  epithelium  are  now  six  or  seven  rows  of  rounded 
nucleated  cells.  It  is  possibly  their  function  to  recruit  the 
former. 

Thus  beginning  from  without  inwards,  the  enamel  organ 
consists  of  (i)  external  epithelium;  (ii)  stellate  reticulum;  (iii) 
stratum  intermedium;  and  (iv)  internal  epithelium.  The  latter, 
soon  to  be  called  ameloblasts  or  enamel  cells,  are  placed  side 
by  side  on  what  would  seem  to  be  a  fine  basement  membrane. 
There  is  no  commencement  of  deposition  of  enamel. 

The  cells  of  the  stratum  intermedium,  according  to  Leon 
Williams,  form  a  layer  in  which  blood-vessels  are  developed 
at  a  very  early  stage.  This  is  well  brought  out  in  the  enamel 
organs  of  rodents.  Here  the  layer  seems  to  be  "a  highly 
differentiated  secreting  tissue."  The  ameloblasts  are  sur- 
mounted by  epithelial  papillae,  around  and  between  which  is 
a  free  distribution  of  capillary  loops.  The  enamel-forming 
cells  are  seen  to  have  an  intimate  relationship  with  the  papillae, 
each  apparently  having  a  root-like  process  which  extends  into 
and  is  lost  within  the  papilla  to  which  it  belongs.  "The 
diameter  of  each  papilla  is  equal  to  about  that  of  five  or  six 
ameloblasts,  and  each  papilla  may  therefore  be  said  to  supply 
from  twenty  to  twenty-five  ameloblasts"  (Fig.  211). 

The  papillae  are  supposed  to  originate  in  spindle-shaped 
cells. 

(viii)  Changes  in  the  Dentine  Papilla 

Meanwhile  the  dentine  germ  is  becoming  highly  spe- 
cialized. The  round  nuclei  of  the  cells  crowd  together,  and 
apparently  are  imbedded  at  the  enamal  surface  in  a  clear 
indefinable  matrix.  The  cells  are  protoplasmic,  minus 
branches;  but  most  deeply  of  all  they  become  fusiform  with  long 
branching  processes,  and  are  continuous  with  similar  cells 
situated  immediately  outside  the  neck  and  the  rotundity  of 
the  enamel  organ.  Furthest  from  the  centre  they  are  very 
narrow,  and  greatly  separated  from  one  another. 

The  alveolar  bone  is,  at  this  time,  extending  towards  the 
surface,  and  is  encroaching  on  the  neck  of  the  enamel  organ. 


246 


DENTAL   HISTOGENESIS 


DP 


FIG.  213. — Further  stage  of  evolution.  Jaw  of  kitten.  Stained  with  haema- 
toxylene.  Magnified  60  times.  Represents  the  stage  of  development  in  man 
at  about  the  poth  day.  D.P.  Dentine  papilla;  S.R.  Stellate  reticulum. 


D  P 


FIG.  214.— Same    as    preceding,    further    developed.     Same    magnification. 

presents  the  stage  of  development  in  man  at  about  the  i2oth  day.  E.  First 
trace  of  enamel ;D.  Calcified  dentine;  D.Z.  Dentogenetic  zone;  D.P.  Dentine  papilla; 
D.C.  Dental  capsule;  A.  Ameloblasts.1 


DEVELOPMENT  OF  TEETH  IN  Mammalia 


247 


B  V 


S  R 


DC 


AB 


DC 


FIG.  215. — Similar  to  the  preceding.  Stained  with  haematoxylene.  Magnified 
80  times.  Represents  the  stage  of  development  in  man  at  about  the  looth  day. 
E.E.  External  epithelium  of  the  enamel  organ;  S.R.  Stellate  reticulum;  s.l. 
Stratum  intermedium;  A.  Ameloblasts;  D.P.  Dentine  papilla;  z.  Tooth  band  of 
permanent  successor;  B.v.  Blood-vessel;  D.C.  Dental  capsule;  A. B.  Alveolar  bone. 


248 


DENTAL   HISTOGENESIS 


B  V 


OE 


V  M 


SR 


FIG.  216. — Vertical  section  through  head  of  Macropus  Billiardieri.  Stained 
with  hasmatoxylene  and  cosine.  Magnified  45  times.  There  is  no  permanent 
tooth  band,  as  Marsupials  are  mon  phyodont.  D.  Dentine;  D. p.  Dentine  papilla; 
s  R.  Stellate  reticulum;  N.  Neck  of  enamel  organ;  B.V.  Blood-vessel;  V.M.  Voluntary 
muscle  of  cheek;  T.  Tongue;  O.E,  Oral  epithelium. 


DEVELOPMENT  OF  TEETH  IN  Mammalia 


249 


Shortly  after  these  changes  have  taken  place,  the  neck  of 
the  enamel  organ  is  attenuated  to  the  thickness  of  two  layers 
of  cells;  and  a  tremendous  increase  in  the  mass  of  the  stellate 
cells  occurs.  The  internal  epithelium  assumes  the  shape  of 
the  ameloblasts,  and  some  of  the  peripheral  papilla  cells  that 
of  the  odontoblasts. 


OE 


FIG.  217. — Further  stage  of  development.  Jaw  of  kitten.  Stained  with 
haematoxylene.  Magnified  50  times.  Represents  the  stage  of  development 
in  man  at  about  the  i4Oth  day.  E.  Early  formation  of  enamel;  A.  Ameloblasts; 
D.  Dentine;  o.  Odontoblasts;  z.  Tooth  band  of  permanent  successor;  O.E.  Oral 
epithelium;  D.P.  Dentine  papilla;  B.  Bone  of  jaw;  D.C.  Rudimentary  dental 
capsule. 

At  the  same  time,  about  the  i4oth  day  in  the  deciduous 
incisors,  the  first  deposition  of  formed  dentine  is  seen,  fol- 
lowed almost  immediately  by  the  darker  line  of  enamel.  The 
external  and  internal  epithelia  are  still  continuous. 


Subsequent  Embryological  Changes 

The  tooth  germ,  at  a  later  stage,  is  lodged  in  a  deep,  wide- 
mouthed  gutter  of  bone.     The  cap  of  calcified  enamel  is  sur- 


250 


DENTAL   HISTOGENESIS 


rounded  by  the  layer  of  ameloblasts— long  columnar  proto- 
plasmic cells  having  prominent  nuclei  at  their  distal  growing 
ends.  They  measure  about  5/4  in  width,  and  vary  in  length 
from  5  M  to  15  or  2o/x.  At  the  base  of  the  dentine  germ  they 
are  cubical  in  shape,  and  here  attain  the  former  smaller 
dimensions. 


SM 


T  P 


FIG.  218. — To  show  early  stage  of  formation  of  enamel  and  dentine.  Pre- 
pared by  the  chromic  acid  method,  stained  with  carmine,  and  imbedded  in 
paraffin-wax.  Magnified  320  times.  D.P.  Dentine  papilla;  o.  Odontoblasts; 
D.  Dentine;  E.  Enamel;  A.  Ameloblasts;  T.P.  Tomes' processes  of  the  ameloblasts; 
S.M.  Stratum  intermedium;  S.R.  Nuclei  of  cells  of  stellate  reticulum.  (Photo- 
micrograph by  Douglas  Gabell.) 

In  places  where  they  are  torn  away  from  the  periphery  of 
the  enamel  they  present  tapering  processes,  "Tomes'  processes." 
This  end  (viz.,  that  directed  towards  the  dentine),  according 
to  Tomes  (op.  cit.  p.  168),  is  slightly  enlarged,  a  fact  demon- 
strated after  treating  an  embryonic  tooth  germ  with  glycerine 
or  other  hygroscopic  reagent.  The  cytoplasm  of  each  amelo- 
blast  is  granular,  and  possesses  also  a  delicate  spongioplasm 
(see  Fig.  240). 

Many  instances  occur  in  which  the  cells  appear  to  be  bounded 


DEVELOPMENT  OF  TEETH  IN  Mammalia  251 

at  either  end  by  lines  of  basement  membrane.  To  these  Leon 
Williams  has  given  the  names  the  "inner  and  the  outer  ^amelo- 
blastic membranes." 


FIG.  219. — Section  of  developing  tooth  of  human  fretus  near  the  seventh 
month  of  intra-uterine  life.  Magnified  175  times.  A.  Outer  epithelial  layer  of 
enamel  organ  in  which  secreting  papillae  are  developed;  B.  andc.  Xumerous  large, 
round,  granular,  nucleated  cells  of  reticulum  of  enamel  organ.  The  stellate 
appearance  in  this  tissue  is  largely  produced  by  shrinkage  and  the  washing 
away  of  the  cell  contents;  D.  Stratum  intermedium;  E.  Outer  ameloblastic 
membrane;  F.  Ameloblasts;  G.  Inner  ameloblastic  membrane;  H.  Dentine;  i. 
Odontoblasts.  (Photomicrograph  by  Leon  Williams.) 


The  former  had  been  previously  described  by  Huxley,  Rasch- 
kow  and  others  as  the  membrana  preformattia. 

Both  membranes  are  structureless  basement  membranes, 
and  are  adherent  to  both  extremities  of  the  ameloblasts. 


2r2  DENTAL    HISTOGENESIS 

The  outer  lies  between  the  ameloblasts  and  the  cells  of  the 
stratum  intermedium;  the  inner  between  the  ameloblasts 
and  the  formed  enamel. 

Leon  Williams  describes  these  membranes  very  carefully 
in  his  contribution  to  The  Dental  Cosmos  for  1896,  pp.  no 


,-E 


FIG.  220. — Section  of  developing  tooth  of  embryo  calf.  Magnified  800  times. 
A.  Outer  ameloblastic  membrane;  B.  Ameloblasts  showing  network  pattern  of 
plasmic  cell  contents;  c.  Strings  of  plasmic  network  passing  through  inner 
ameloblastic  membrane;  D.  Dentine;  E.  Chromatin  of  nuclei  of  odontoblasts; 
F.  Spongioplasm  of  odontoblasts.  (Photomicrograph  by  Leon  Williams.) 


et  seq.:  "It  is  impossible  at  present  (1896)  to  speak  definitely 
with  reference  to  its  (the  outer  membrane)  origin,  exact  struc- 
ture, or  function.  Its  appearance  at  the  ends  of  the  cells  and 
not  between  them  would  seem  to  argue  against  the  suggestion 
that  it  is  due  to  a  condensation  of  the  peripheral  zone  of  the 


DEVELOPMENT  OF  TEETH  IN  Mammalia  253 

cells.  But  this  view  is  supported  by  the  fact  that  it  is  not  seen 
during  the  earlier  periods  of  the  tooth  germ;  but  only  after  the 
nearly  or  quite  complete  specialization  of  the  ameloblasts." 
Under  high  powers  it  is  composed  of  more  than  a  single  layer; 


FlG.  221. — To  show  arrangement  of  parts  in  the  enamel  organ.  Stained 
with  hasmatoxylene.  Magnified  300  times.  D.  Dentine;  E,  Enamel;  A.  Amelo- 
blasts; I.  Inner  ameloblastic  membrane;  o.  Outer  ameloblastic  membrane; 
S.M.  Stratum  intermedium;  s.R.  Stellate  reticulum. 


and  "it  is  possible  that  it  plays  an  important  part  in  the  elabora- 
tion of  material  for  enamel  building.  It  varies  considerably 
in  thickness  in  different  specimens,  but  persists  throughout  the 
entire  period  of  enamel  formation — a  fact  which  would  seem 


254 


DENTAL   HISTOGENESIS 


FIG.  222. — Section  of  developing  tooth  of  human  embryo.  Magnified  1,000 
times.  A.  Cells  of  stratum  intermedium  showing  structure  of  nuclei.  B. 
Ameloblasts;  c.  Enamel-globules  showing  radiating  processes;  D.  Dentine;  E. 
Odontoblasts  showing  chromatin  of  nuclei.  (Photomicrograph  by  Leon  Williams.) 


DEVELOPMENT  OF  TEETH  IN  Mammalia  255 

to  give  a  decided  negative  to  the  theory  that  the  ameloblasts 
are  renewed  from  the  stratum  intermedium,  as  many  writers 
on  the  subject  have  supposed." 

The  free  surface  of  enamel  has  a  pitted  or  honey-combed 
outline,  whence  the  Tomes'  fibres  have  been  withdrawn;  the 
rest  is  almost  homogeneous. 


PS 


FIG.  223. — Similar  to  Fig.  221.     p.s.   Pitted  surface  of  enamel;  c.   Calcoglobular 
mass  in  an  ameloblast. 


Not  so,  however,  the  dentine,  for  traces  of  its  tubular  nature 
can,  even  at  this  early  stage  of  growth,  be  easily  observed  in 
sections  stained  with  Ehrlich's  acid  hccmatoxylene  in  its  cal- 
cified (external),  and  less  clearly  in  the  formed  but  as  yet  un- 
calcified  portions. 

The  superficial  mesodermic  cells  of  the  papilla,  before  the 
formation  of  the  odontoblasts,  are  arranged  with  a  certain 
amount  of  regularity,  with  their  long  axes  pointing  towards 
the  ameloblasts.  These  in  their  growth  become  elongated, 
the  result  being,  according  to  Paul  (op.  cit.},  the  formation  of 
a  definite  superficial  zone. 


256 


DENTAL   HISTOGENESIS 


Their  nuclei  are  "resting"  (see  Fig.  101). 

Later  on  the  odontoblasts  themselves  begin  to  appear 
among  these  superficial  cells,  the  nuclei  of  which,  passing 
from  the  resting  stage,  undergo  atrophy. 

The  remainder  of  the  papilla  is  made  up  of  branched  con- 
tinuous cells. 

Shortly  after  the  fusiform  connective  tissue  cells,  which  go 
to  make  up  the  dental  capsule  or  follicle,  have  become  con- 


FIG.  224. — Vertical  section  through  mandible  of  human  foetus  at  about  the 
i6oth  day  of  intra-uterine  life.  Shows  base  of  decidnous  canine  tooth.  Pre- 
pared as  usual  with  soft  tissues.  Stained  en  masse  in  borax-carmine.  Cut  in 
paraffin-wax.  Magnified  50  times.  B.  Base  of  dentine  papilla;  H.  Epithelial 
sheath  of  Hertwig. 


tinuous  round  the  whole  tooth  germ,  the  investing  stellate 
reliculum  begins  to  disappear.  The  first  stage  in  its  atrophy 
and  absorption  is  the  disappearance  of  the  nuclei  of  these 
cells.1  The  external  epithelial  cells  become  somewhat  separated, 
but  connected  still  with  the  branches  of  the  stellate  reticulum 

1  The  stellate  reticulum  persists  longest  in  the  intervals  between  the  cusps  of  the 
molar  teeth. 


DEVELOPMENT  OF  TEETH  IN  Mammalia 


257 


on  the  one  hand  and  the  elongated  cells  of  the  dental  capsule 
on  the  other.  The  ameloblasts  reach  their  highest  degree  of 
development  over  the  cusps  of  the  dentine  germ,  and  the 
enamel  is  being  rapidly  manufactured.  The  dentinal  wall  of  the 


o  E 


p  z 
A 


E  E 


FIG.  225. — Vertical  section  through  jaw  of  pulp  at  birth.  Prepared  in  the 
usual  way.  Stained  with  Ehrlich's  acid  haematoxylene.  Magnified  45  times. 
Represents  the  stage  of  development  in  man  at  about  the  i4Oth  day.  O.K.  Oral 
epithelium;  A.  Ameloblasts;  E.  Enamel;  D.  Dentine;  o.  Odontoblasts;  D.P.  Dentine 
papilla;  s.R.  Stellate  reticulum;  E.E.  External  epithelium;  D.S.  Dental  capsule;  B. 
Bone  of  jaw;  p.z.  Tooth  band  of  permanent  tooth  germ;  M.  Voluntary  muscle 
fibres  cut  transversely. 

tooth  germ  is  lengthening  towards  the  base  of  the  dentine  germ, 
which  shows  signs  of  constriction  by  the  approximation  of  the 
cells  of  the  internal  epithelium. 

At    the    extreme   point   they   suddenly  curve  upwards  and 
outwards,   and  thus  form  the  epithelial  sheath  of  Hertwig. 
17 


258 


DENTAL   HISTOGENESIS 


The  cells  of  the  dentine  germ  possess  the  same  histological 
characteristics,  except  those  on  the  surface  of  the  pulp,  which, 


\ 


p  z 


DS 


FIG.  226. — Coronal  section  through  the  maxilla  of  a  foetal  pig.  Prepared  and 
stained  as  in  last  figure.  Magnified  the  same.  Represents  the  stage  of  develop- 
ment in  man  at  about  the  i2Oth  day.  Lettering  as  in  Fig.  225. 

as  the  so-called  odontoblasts,  are  clearly  differentiated  in 
size,  shape,  and  staining  properties  from  the  other  connective 
tissue  cells. 


DEVELOPMENT  OF  TEETH  IN  Mammalia 


P  V 


SR 


FIG.  227. — Coronal  section  through  the  mandible  of  a  kitten.  Stained  with 
borax-carmine  after  hardening  in  formic  aldehyde.  The  blood-vessels  are 
naturally  injected.  Represents  the  stage  of  development  in  man  at  about  the 
i6othday.  Magnified  65  times.  E.  Enamel;  D.  Dentine;  S.R.  Stellate  reticulum; 
p.v.  Blood-vessels  in  the  pulp;  L.  Loops  of  capillaries  extending  to  the  external 
epithelium  of  the  enamel  organ. 


260 


DENTAL   HISTOGENES1S 


M  N 


FIG.  228. — Vertical  section  of  mandible  of  pup  at  birth.  Stained  with 
h sematoxylene.  Magnified  30  times.  About  same  age  as  preceding  figure. 
R  Early  formation  of  a  root;  M.N.  Mandibular  nerve,  with  accompanying 
artery  and  veins. 


DEVELOPMENT  OF  TEETH  IN  Mammalia  261 

(ix)  Evolution  of  the  Permanent  Tooth  Germs 

About  this  period  sections  show  the  epithelial  inflection 
which  goes  to  form  the  successional  tooth,  which  is  but  the 
growing  or  free  end  of  the  tooth  band,  and  not  a  budding 
from  the  neck  of  the  enamel  organ  of  the  deciduous  tooth 
germs.  Rose  has  proved  this  fact  beyond  doubt.  This 
neck  has  now  completely  vanished. 

Subsequently  the  tooth  germ  assumes  the  shape  of  the 
future  tooth.  The  enamel  organ  has  gone;  the  calcified  den- 
tine and  dentogenetic  zone  surround  the  young  pulp.  The 
thickness  of  the  enamel  cap  has  increased;  the  regularly 
arranged  ameloblasts  and  stratum  intermedium  cells  are  very 
pronounced,  and  nothing  intervenes  between  the  oral  epi- 
thelium and  the  stratum  intermedium  but  a  large  amount 
of  submucous  tissue,  composed  of  long  branching  fusiform 
connective  tissue  cells  imbedded  in  a  thin  stroma,  which  also 
contains  blood-vessels,  and  at  times,  tiny  masses  of  epithelium 
("Glands  of  Serres").  The  latter  are  derived  from  the  rem- 
nants of  the  fenestrations  of  the  tooth  band.  The  former 
seem  to  run  right  down  to  the  condensed  papillary  tissue  on 
the  surface  of  the  stellate  reticulum,  as  if  they  were  carrying 
special  nutritive  material  to  this  region. 

In  the  young  pulp,  the  walls  of  the  blood-vessels  and  rudi- 
mentary myelinic  nerve  fibres  make  their  appearance,  the 
first  by  the  approximation  and  joining  up  of  the  branching 
process  of  the  longer  cells,  running  singly  in  a  line,  the  sec- 
ond by  the  development  of  the  cells  in  longitudinal  bundles. 

The  vascularity  or  otherwise  of  the  enamel  organ  is  not  yet 
determined,  many  competent  authorities  holding  opposite 
opinions  on  this  subject.  Thus  Lionel  Beale,  Leon  Williams, 
Howes,  and  Paulton  assert  that  a  vascular  network  is  to  be 
found  in  the  stratum  intermedium,  while  Tomes,  Paul,  An- 
drews, Wedl,  Sudduth,  and  Magitot  affirm  its  non-vascularity. 

The  author  in  a  joint  paper  with  H.  W.  Marett  Tints  has 
recently  described  the  presence  of  blood-vessels,  containing 
erythrocytes  in  the  enamel  organ  of  the  Australian  wallaby. 


262  DENTAL   HISTOGENESIS 

("Tooth  Germs  in  the  Wallaby,  Macropus  billiardieri."     Proc. 
Zoolog.  Soc.,  London,  1911.) 

(x)  The  Blood  Supply  of  the  Developing  Dental  Tissues 

In  determining  the  relationship  which  normally  exists 
between  the  vascular  supply  of  the  dental  tissues  and  the  tis- 
sues themselves,  it  is  necessary  to  consider  the  origin  of  the 
blood-vessels,  their  arrangement  and  mode  of  distribution, 
and  the  areas  supplied  by  them.  Where  great  development 
is  taking  place  there  is  a  free  blood  supply,  and  the  more  com- 
plex the  organisation  of  a  part — whether  in  anatomical  struc- 
ture or  location  or  in  physiological  function — the  more  abun- 
dant anastomosis  of  capillary  blood-vessels  is  found.  And 
this  anastomosis  is  most  important  in  controlling  the  growth 
of  the  tissue,  as  on  it  depends  the  hypertrophy,  or  atrophy, 
or  normal  conditions  of  the  part.  For  should  the  blood  stream 
be  increased  or  accelerated,  then  overgrowth  results;  while, 
on  the  other  hand,  should  it  be  diminished  or  occluded,  it  is 
followed  by  shrinkage,  atrophy,  degeneration,  and  death. 

Hence  the  blood  supply  of  the  hard  and  soft  dental  tissues 
is  of  vital  importance;  when  normal,  the  tooth  undergoes 
the  changes  consequent  on  evolution,  and,  finally,  is  erupted 
in  a  perfect  condition;  when  abnormal,  hypertrophies  and 
atrophies  of  the  whole  or  parts  of  the  teeth  are  produced, 
and  irregularities  of  external  configuration,  defects  in  quality 
of  the  organic  and  inorganic  substances  and  other  deviations 
from  typical  forms  occur. 

The  most  useful  subject  for  the  purposes  of  the  examination 
of  the  capillary  arrangement  is  an  injected  section,  in  which 
the  functional  activity  of  development  is  most  progressive, 
and  most  clearly  discernible — a  section  whose  genetic  cells  are 
most  busily  engaged  in  producing  the  various  dental  and 
peri-dental  structures — a  section,  in  short,  which  exhibits 
the  birth  of  the  life-history  of  a  tooth. 

Here  it  is  found  that  the  tissues  formed  from  each  layer  of 
the  primitive  blastoderm  are  supplied  by  separate  sets  of 
vessels.  There  is  (i)  an  external  or  superficial,  and  (ii)  an  inter- 
nal or  deep  network,  the  former  being  distributed  to  the  tissues 


DEVELOPMENT  OF  TEETH  ix  Mammalia  263 

which  are  ectodermic  in  origin,  including  gum  and  certain  parts 
of  the  enamel  organ;  the  latter  to  those  arising  from  the  meso- 
derm,  including  dentine  papilla,  dental  capsule  and  surround- 
ing bone.  Thus,  the  external  set  of  vessels  is  distinctly  sepa- 
rated from,  and  has  no  connection  with,  the  internal  deeper 
set,  except  at  one  part,  viz.,  the  periodontal  membrane,  where 
they  meet  and  anastomose  freely  (see  Plate  I). 


-^^n^^^^ 

FIG.  229. — A  portion  of  the  blood  supply  of  the  stratum  intermedium  of  the 
enamel  organ  of  the  section  photographed  in  Fig.  227.  Magnified  300  times. 
The  staining  was  unsuited  to  reveal  the  structure  of  the  ameloblasts;  but  it 
displays  the  erythrocytes  which  have  been  retained  in  situ. 

(i)  The  external  set  supplies  the  enamel  organ  and  gum. 
On  examination  of  the  enamel  organ  proper,  it  is  found  that 
its  external  part  is  absolutely  free  from  any  closely  meshed 
network  of  capillaries.  The  layer  of  cells,  forming  the  ex- 
ternal epithelium  and  the  thin  branching  cells  of  the  stellate 
reticulum  have  no  blood  supply.  One  or  two  large  non-branch- 
ing vessels  traverse  the  space  occupied  by  the  reticulum,  from 
the  thick  gum  and  connective  tissues  lying  external  to  the 
enamel  organ.  These,  having  advanced  as  far  as  the  stratum 
intermedium,  suddenly  break  up  into  numbers  of  small  capil- 


264  DENTAL   HISTOGENESIS 

laries,  and  form  a  beautiful  plexus  which  supplies  the  cells  of 
this  intermediate  layer  and  the  internal  epithelium. 

But  the  capillaries  are  placed  very  closely  together  over 
the  layer  of  ameloblasts — a  fact  explained  by  the  activity  and 
importance  of  these  cells  in  the  formation  of  enamel  and  their 
consequent  necessity  for  a  large  supply  of  blood. 

Little  need  be  said  of  the  vessels  of  the  gum.  The  stratum 
corneum,  lucidum,  and  granule  sum  are  non-vascularised:  the 
rete  Malpighii  and  fibrous  connective  tissue  of  the  dermis 
differing  greatly  by  being  abundantly  provided  with  numerous 
straight,  long  vessels  which  ramify  in  every  direction.  It  is 
clear,  therefore,  that  the  nourishment  of  enamel  organ  and 
fibrous  tissue  of  the  gum  emanates  from  the  same  source,  and 
is  quite  differentiated  from  that  of  the  other  dental  structures. 

(ii)  The  internal  set  supplies  the  dentine  organ,  dental  capsule, 
and  surrounding  bone. 

In  the  dentine  organ,  the  pulp  has  by  far  the  largest  and 
most  important  system  of  blood-vessels.  Here,  one  large  vessel 
enters  at  the  apical  foramen  of  the  tooth,  and  occupying  its 
longitudinal  axis,  passes  sinuously  outwards,  to  end  near  the 
newly  formed  dentine.  As  it  proceeds,  its  calibre  becomes 
somewhat  diminished  in  size,  and  in  a  thick  plexus  of  vessels 
its  branches  terminate  beneath  the  odontoblasts,  some  run- 
ning, in  adult  pulps,  into  the  basal  layer  of  Weil.  There  appears 
to  be  no  definite  regularity  in  the  arrangement  of  the  primary 
branches:  they  leave  the  large  arterial  trunk  at  a  considerable 
angle — in  some  sections  this  approaches  to,  even  if  it  does  not 
exceed,  a  right  angle.  The  secondary  and  other  branches  have 
a  similar  arrangement.  The  greater  number  of  the  minor  distal 
branches  run  parallel  to  the  dentogenetic  zone  under  cover  of  the 
odontoblasts,  between  and  around  which  their  ultimate  ramifi- 
cations are  distributed.  These  cells  and  the  small  round  pulp 
cells  which  lie  closely  to  them,  have,  therefore,  an  abundant 
supply  of  blood,  brought  about  in  a  similar  manner  to  that 
which  obtains  in  the  cells  of  the  stratum  intermedium,  and  inter- 
nal epithelium. 

The  comparative  size  of  these  pulp  vessels  is  much  greater 
than  that  of  the  fine  closely  set  capillaries  of  voluntary  muscle 


DEVELOPMENT  OF  TEETH  IN  Mammalia  265 

fibres;  they  bear  a  slight  analogy  to  them,  but  none  of  the  vari- 
cosities  or  spherical  dilatations  found  on  the  walls  of  the  latter 
are  to  be  observed  in  the  former. 

The  advantages  of  this  peculiar  method  of  arrangement — 
the  sinuous  primary  arterial  trunk,  the  branches  coming  off 
at  right  angles,  the  minute  anastomosis  beneath  the  dentine — 
are  manifest  at  once.  It  is  evident  that  they  are  thus  distrib- 
uted, first,  to  give  as  large  an  area  of  blood  supply  to  the  pulp 
tissues  in  as  small  a  space  as  possible;  and,  second,  to  prevent 
shock  or  any  other  extraneous  influence  from  acting  injuriously 
on  its  delicate  elements.  In  this  manner,  a  flow  of  blood  to  the 
part  is  maintained — constant  and  uniform,  two  necessary 
factors  in  the  production  of  perfect  development,  growth,  and 
nourishment. 

There  is  no  collateral  circulation  in  the  dental  pulp. 

Included  in  the  term  "dental  capsule"  at  this  period  of  the 
genesis  of  the  tooth,  are  its  products,  the  cementum  and  perio- 
dontal  membrane. 

It  is  difficult  to  determine  absolutely  whence  and  how  the 
cementum  is  nourished.  It  would  seem  to  come  chiefly  from 
the  periosteal  vessels.  That  trophic  influences  are  exercised 
upon  it  to  a  certain  but  limited  extent,  is  an  undoubted  fact,  and 
it  is  equally  certain  that  the  dentine  is  not  the  medium  by 
which  they  come.  Hence  it  is  fair  to  presume  that  the  same 
vessels  which  supply  the  alveolo-dental  membrane,  vitalize 
the  tissue  by  means  of  an  exudation  of  lymph  through  their 
walls,  which  passes  into  it  via  the  channels  which  contain 
Sharpey's  perforating  fibres.  It  may  be  assumed,  however, 
that  cementum  is  practically  devoid  of  nutrition. 

Wedl1  was  the  first  to  demonstrate  that  the  dental  perios- 
teum has  three  sources  for  its  blood  supply,  viz. :  (a)  from  the 
gum,  (6)  from  the  pulp,  and  (c)  from  the  adjacent  bone  of  the 
alveolar  process. 

In  regard  to  the  first,  it  has  already  been  shown  that  the 
external  and  internal  sets  unite  in  this  situation,  the  vessels 
of  the  gum  running  downwards  to  anastomose  with  the 

1  "Pathologic  dcr  Zahne,"  1870. 


266  DENTAL   HISTOGEKESIS 

internal  set  which  supplies  the  dental  capsule.  But  also  loops 
of  capillaries  from  the  main  arterial  trunk  of  the  pulp,  before  it 
enters  that  organ,  can  be  seen  spreading  outwards  and  joining 
the  before-mentioned  vessels  (see  F,  in  Plate  I).  And  in 
addition,  numerous  offshoots  from  the  capillaries  of  the  alveolar 
bone  run  towards  the  cementum,  and  form  thick  plexuses 
with  the  other  two.  The  periosteum  is,  therefore,  most  richly 
vascularised,  and  forms  by  its  method  of  attachment  the 
vascular  bridge,  so  to  speak,  between  the  living  tissues  of  the 
jaw  and  the  tissues  of  the  tooth. 

The  vascularisation  of  the  bone  of  the  alveolus  calls  for  no 
further  comment  here,  being  identical  with  the  blood  supply 
of  cancellous  bone  elsewhere. 

Briefly,  to  summarise,  it  can  be  said  with  tolerable  cer- 
tainty that  of  the  soft  tissues,  the  pulp  as  being  the  most 
important  nutritive  agent,  has  the  greatest,  and  the  gum  the 
smallest  system  of  capillaries;  while  in  the  enamel  organ  the 
reticulate  cells,  and  the  external  epithelium  are  destitute  of 
any  vessels  whatsoever. 

An  examination  of  the  section  from  a  photomicrograph  of 
which  Fig.  227  is  reproduced,  shows,  however,  that  while  blood- 
vessels do  not  actually  anywhere  pierce  the  stellate  reticulum, 
yet  long  capillaries  run  freely  everywhere  immediately  out- 
side the  external  epithelium;  and  where  this  is  closely  applied 
to  the  stratum  intermedium  (the  intervening  stellate  tissue 
being  atrophied),  the  numbers  and  size  of  the  capillaries  are 
greatly  increased.  This  must  not  be  interpreted,  however, 
as  signifying  complete,  but  only  as  a  modified  form  of  vasculari- 
sation of  the  enamel  organ. 

The  cells  of  the  internal  epithelium  must  obtain  a  free 
blood  supply  from  somewhere,  for  the  purpose  of  manu- 
facturing the  calcine  basis  of  enamel,  and  it  is  difficult  to  con- 
ceive of  this  physiological  phenomenon  occurring  as  a  product 
of  cells  which  have  no  contiguity  whatever  with  the  vascular 
system  of  the  body. 

An  important  addition  to  the  literature  of  the  vascular 
supply  of  the  teeth  of  man  comes  from  the  pen  of  Dr.  W. 
Lepkowski,  of  Cracow.  Following  up  original  work  on  in- 


DEVELOPMENT  OF  TEETH  IN  Mammalia  267 

jected  preparations  of  the  teeth  of  the  lower  placental  verte- 
brates, there  appeared  an  interesting  article  on  "The  Distribu- 
tion of  the  Blood-vessels  in  the  teeth  of  Man"  in  the  "Anato- 
mische  Hefte."1 

"In  a  foetus  of  seven  months  the  alveolar  artery  provides 
one  branch  for  each  tooth  germ  which  is  thus  entered  at  its 
base.  The  artery  directly  before  its  entrance  into  the  sac  is 
still  to  be  recognised  as  such,  and  can  be  easily  distinguished 
from  the  veins  accompanying  it.  Further  on,  the  walls  of 
the  artery  become  so  thin  that  even  in  stained  preparations 
they  can  no  longer  be  distinguished  from  the  two  veins  ac- 
companying it.  The  vessel  now  rises  to  the  highest  part  of 
the  pulp  and  there  divides  into  a  number  of  branches,  which 
spread  out  in  a  fan-like  fashion  from  the  base  to  the  apex  of 
the  tooth  germ.  These  branches  are  really  capillaries.  They 
proceed  between  the  odontoblasts  up  to  the  dentine  and  there 
form  broad  loops  which  unite  with  each  other.  As  has  already 
been  described  in  animals,  there  also  spreads  out  in  man,  on 
the  surface  of  the  pulp  between  the  odontoblasts,  a  broad  net 
of  capillaries,  which  is  distinguished  from  the  remaining  woof 
running  through  the  pulp  by  its  breadth  and  density.  An 
examination  of  numerous  sections  teaches  one  that  the  distribu- 
tion of  this  capillary  net  is  not,  however,  the  same  on  the  whole 
surface  of  the  pulp.  At  the  base  of  the  tooth  the  vascular 
anastomosis  is  always  denser  and  more  interwoven  than  to- 
wards its  apex,  where  the  net  becomes  comparatively  broader 
and  looser.  This  arrangement  of  the  vessels  follows  the  ar- 
rangement of  the  odontoblasts.  With  low  magnifying  power 
there  can  be  seen,  in  preparations  stained  with  carmine,  a 
broad  band  of  odontoblasts  at  the  base  of  the  tooth  germ  just 
where  the  vessels  also  are  present  in  greater  numbers;  towards 
the  top  of  the  tooth  germ  the  breadth  of  the  odontoblast  layer 
decreases  appreciably,  and  simultaneously  the  network  of  the 
vessels  becomes  looser.  It  can  scarcely  be  doubted  that  both 
appearances  are  connected  with  each  other.  It  is  also  easily 
to  be  explained  why  at  the  base  of  the  tooth  germ  the  vessels 

1  "Die  Verteilung  der  Gefasse  in  den  Zahnen  des  Menschen,"  Weisbadcn,  1901. 


268  DENTAL   HISTOGEXESIS 

and  odontoblasts  are  more  closely  arranged  than  elsewhere; 
for  it  is  on  the  base  of  the  tooth  that  new  substance  is  deposited, 
and  the  vessels  and  odontoblasts  (sic)  are  chiefly  concerned  in 
this  process.  As  this  distribution  of  the  vessels  and  cells  can  be 
seen  in  every  preparation,  we  may  consider  this  kind  of  arrange- 
ment as  the  rule  in  the  formation  of  teeth.  In  reference  to  the 
mutual  relationship  between  capillaries  and  odontoblasts,  it 
may  be  mentioned  that  the  former,  as  loops,  reach,  between  the 
odontoblasts,  up  to  the  dentine  layer.  They  take  no  direct 
share  in  the  formation  of  the  dentinal  tubes.  On  the  other  hand, 
we  must  assume  that  they  convey  the  necessary  material  for 
the  building  up  of  the  tooth  and  induce  special  activity  of  the 
odontoblasts.  The  dense  distribution  of  the  vessels  at  the 
surface  of  the  pulp,  between  the  odontoblasts  generally,  as 
also  specially  at  the  basal  parts  of  the  tooth  germ,  points  to  this. 

"If  we  compare  the  vascular  systems  in  the  various  teeth 
of  the  same  embryo,  we  obtain  deviations  according  to  the 

number  of  the  roots  and  the  form  of  the  tooth  crown 

If  we  take  a  section  through  a  single  root  tooth  germ — for 
example,  a  canine — we  get,  in  the  centre  of  the  pulp,  a  bundle  of 
vessels,  which  after  their  sub-division  into  finer  ramifications 
provide  for  the  entire  pulp,  and  under  the  dentine  spread  out 
in  a  characteristic  manner.  In  the  germ  of  a  two-cusp  tooth 
there  are  present  two  bundles  of  vessels  separated  from  each 
other.  From  this  we  get  the  impression  that  the  tooth  had 
been  developed  from  a  number  of  single  teeth  corresponding 
to  the  cusps  and  roots.  A  series  of  sections  obtained  from  the 
tooth  germ  of  a  three-rooted  molar  favours  the  proposition  still 
more.  We  see,  therefore,  in  the  first  sections  two  bundles  of 
vessels  and  two  cusps.  The  vascular  bundles  enter  separately 
at  the  base  of  the  tooth  germ,  and  only  in  their  ramifications 
in  the  tooth  pulp  do  they  become  connected  with  each  other." 

As  a  carollary  to  this  line  of  argument  this  author  formulates 
the  following  highly  interesting  theory:  "I  believe  that  my 
results  on  the  distribution  of  the  vessels  in  developing  molars 
speak  in  favour  of  the  hypothesis  advanced  by  various  inves- 
tigators, among  them  Dybowski  and  Rose  ('Ergebnisse  der 
Anat.  und  Entwickelungsgeschichte,'  1899),  that  the  het- 


DEVELOPMENT  OF  TEETH  IN  Mammalia  269 

erodont  set  of  teeth  of  man  and  mammals  has  originated  from  a 
homodont  dental  apparatus.  The  individual  cone-shaped  teeth 
such  as  exist  to-day  in  reptiles,  becoming  approximated  through 
the  shortening  of  the  maxilla,  fuse,  so  to  speak,  and  form  com- 
pound teeth,  which  according  to  their  function  and  the  devel- 
opment of  the  osseous  parts  surrounding  them,  in  the  course 
of  time,  receive  their  present  shape.  The  witness  for  their 
descent  from  simple  teeth  is  to  be  sought  for  in  the  rudiments 
of  several  cusps,  and  their  separate  vascular  supply  during 
their  development.  Not  much  reliance  must  be  placed  upon 
the  number  of  roots  with  which  they  are  provided.  As  already 
stated,  this  is  as  a  rule  reduced,  perhaps  in  consequence  of 
mechanical  influences.  Besides,  as  is  known,  there  are  often 
found  four,  five,  or  even  six  roots  on  molars.  Their  presence 
proves  that  corresponding  to  the  number  of  cusps  under  fav- 
ourable conditions  they  may  continue  to  exist  in  their  original 
type  without  reduction,  of  course,  as  rudiments,  of  the  former 
homodont  masticating  apparatus. 

"The  vessels  which  externally  surround  the  enamel  organ 
are  connected  with  the  pulp-vessels.  The  vessels  originate  in 
the  inter-alveolar  arteries  which  supply  the  cancellous  bone 
substance  of  the  maxillae.  They  spread  out  in  a  dense  woof 
at  the  surface  of  the  enamel  organ,  but  do  not,  however, 
penetrate  between  the  ameloblasts  of  the  enamel  organ. 
To  judge  from  microscopical  sections  they  belong  to  the 
venous  system.  They  surround  the  tooth  germ  from  the 
first  rudiments  of  its  development.  Notwithstanding  that  they 
deviate  from  the  method  of  arrangement  of  the  pulp-vessels, 
they  agree  with  the  latter  in  so  far,  in  a  physiological  sense, 
that  they  play  an  active  part  in  the  formation  of  the  enamel,  as 
the  others  have  an  active  share  in  the  formation  of  dentine. 
On  thorough  examination  of  the  preparations,  it  is  observed 
that  at  the  apices  of  the  tooth-germs  where  the  enamel  is  thick- 
est, the  vascular  net  is  also  denser.  The  points  correspond  to 
the  highest  parts  of  the  tooth.  When  the  tooth  crown  is  near 
its  completion,  the  activity  of  the  enamel  cells  gradually  ceases, 
and  the  vessels  supplying  them  slowly  undergo  retrogressive 
changes.  Within  the  tooth,  however,  the  formative  activity 


270 


DENTAL   HISTOGEXESIS 


of  the  odontoblasts  and  the  blood-vessels  still  continues,  until 
the  dentine  of  the  crown  and  the  roots  has  been  built  up. 

"The  disappearance  of  the  vessels  of  the  enamel  organ 
begins  at  the  summit  of  the  tooth,  and  proceeds  in  the  direction 
of  the  root.  In  the  stages  of  evolution,  in  which  the  tooth  is 
erupted,  the  superficial  vessels  unite  with  those  of  the  gum; 
those  lying  deeper  surround  the  root  and  supply  its  newly 
formed  periodontal  membrane.  They  spread  out  on  the  walls 
of  the  alveolus,  and  remain  in  this  position,  as  long  as  the 
tooth  exists.  ...  Of  the  pulp-vessels,  individual  vessels  or 
also  bundles  of  them  occasionally  separate,  perforate  in  places 
the  dentine-layer  and  the  enamel-layer  and  obtain  connection 
with  vessels  surrounding  the  tooth  germ  on  the  outside.  Ex- 
amples of  such  vascular  connections  I  have  observed  in  tooth 
preparations  of  the  embryos  of  the  lower  animals,  as  also  in 
those  of  man. 

"On  examining  such  sections  one  might  be  tempted  to 
think  of  an  analogy  with  the  Haversian  canals  in  bones.  How- 
ever, the  vascular  connections  of  the  kind  mentioned  are  too 
rare  to  be  looked  upon  as  quite  normal  formations.  I  believe 
I  can  explain  in  another  way  this  vascular  communication 
which  arises  but  rarely. 

"In  later  stages  of  development,  and  in  adult  man,  one 
finds  at  the  lateral  surfaces  of  the  teeth,  and  more  especially 
on  the  molars,  a  funnel-shaped  constriction.  In  sections, 
made  transversely  through  the  tooth  at  the  level  of  such  a 
depression,  one  observes  the  dentine  tubes  markedly  condensed, 
as  it  were,  as  if  there  were  present  a  scar  in  the  dentinal  tissue, 
which  reached  up  to  the  pulp  cavity. 

"In  my  opinion  these  cicatricial  formations  in  the  developed 
tooth  are  related  to  the  vascular  communications  just  de- 
scribed. I  myself,  during  my  researches  on  fully  formed  teeth 
have  never  seen  any  other  formations  than  this  cicatricial 
contraction,  but  Thiel  mentions  a  case  which  tells  in  favour 
of  my  view.  Scheff  cites  the  same  case  in  his  'Handbuch' 
when  discussing  haemorrhage  after  extractions.  After  the 
extraction  of  the  first  upper  premolar  on  the  right  side,  con- 
siderable bleeding  followed,  which,  on  careful  examination, 


DEVELOPMENT  OF  TEETH  IN  Mammalia  271 

was  traced,  from  the  wall  of  the  alveolus,  to  a  bundle  of  vessels 
which  entered  the  tooth  at  the  neck  and  ran  transversely 
through  the  dentine  up  to  the  pulp.  At  the  outset  it  is  not  to 
be  assumed  that  the  vessels  in  the  case  mentioned  above 
originally  perforated  the  fully  formed  tooth,  because  the  tooth 
substance  in  advanced  life  is  too  hard  to  allow  blood-vessels  to 
penetrate,  and,  on  the  other  hand,  the  vascular  supply  at  that 
period,  in  comparison  with  that  of  a  younger  age,  is  too  slight." 

Lepkowski  holds  that:  "If  we  compare  the  vascular  dis- 
tribution in  the  teeth  of  man  with  that  of  mammals,  such  as  the 
pig,  the  horse,  and  the  rabbit,  we  find,  what  was  to  be  expected, 
that  there  are  no  appreciable  differences.  The  course  of  the 
vessels,  their  distribution,  the  density  of  the  vascular  net  at 
corresponding  places,  and  its  relationship  to  the  tissues  in 
course  of  formation,  are  the  same  here  as  there.  The  more 
pronounced  differences  are  in  the  number  of  the  vessels  in  the 
tooth  germ.  In  embryos  of  the  animal  species  cited,  there 
exists  in  the  pulp,  as  also  specially  in  the  enamel  organ,  far 
richer  vascular  ramifications  than  in  the  corresponding  teeth  of 
human  embryos.  The  explanation,  to  my  idea,  is  not  far  to 
seek.  There  exist  very  considerable  differences,  first,  in  the 
relative  size  of  individual  teeth  between  animals  and  man 
(for  example,  the  canine);  and  secondly,  in  the  thickness  of 
the  layers  of  substance.  In  the  dog  the  thickness  of  the 
enamel  layer  surpasses  by  far  that  of  the  human  teeth.  It 
is,  therefore,  quite  natural  that  the  tooth  germs  of  animals 
are  provided  more  richly  with  vessels. 

"Otherwise  the  vascular  distribution  from  embryological 
periods  up  to  the  complete  development  of  the  teeth  is,  in 
its  fundamental  characteristics,  analogous  in  man  and  ani- 
mals. The  observations  also  which  I  have  made  in  regard 
to  the  relationship  of  vessels  to  the  cusps  and  roots  in  human 
teeth  may  be  similarly  applied  to  the  teeth  of  animals." 

The  subject  is  one  of  importance,  and  invites  greater 
attention  than  has  hitherto  been  accorded  to  it.  It  should 
not,  however,  be  so  difficult  a  matter  to  determine  in  these 
latter  days;  since  the  modern  introduction  into  the  methods 
of  Dental  Microscopy,  of  solutions  of  formic  aldehyde,  as  a 


272 


DENTAL   HISTOGENESIS 


fixing  and  hardening  agent,  has  shown  that  the  natural  in- 
jection of  blood-vessels  by  blood  cells  can  be  maintained  almost 
exactly  as  during  life. 

(xi)  Final  Stages  of  Evolution 

Later  phases  in  the  evolution  of  the  teeth  include  the 
growth  of  enamel  and  dentine,  the  approximation,  to  the  sur- 
face of  enamel,  of  the  external  epithelium  as  the  cellular  layer 
of  Nasmyth's  membrane,  and  the  complete  organization  of 
the  dental  capsule. 

(xii)  Dental  Capsule 

As  a  thick  investing  fibrous  belt  this  structure  envelopes 
the  whole  of  the  tooth,  except  at  the  apex  of  its  root.  Each 
tooth  has  its  own  capsule:  and  each  capsule  has  a  separate 
entity.  At  first  consisting,  as  has  already  been  pointed  out,  of 
layers  of  flat  fusiform  cells,  round  cells  begin  to  be  formed 
within  it.  These  move  in  an  inward  direction,  and  assume 
the  shape  and  functions  of  ordinary  osteoblasts.  The  result 
of  their  activity  is  to  deposit  cemental  matrix,  which,  about 
the  times  of  the  completion  of  the  crowns  of  the  teeth,  becomes 
intimately  and  securely  applied  to  the  external  periphery 
of  the  dentine.  These  cells  probably  pour  it  out  as  a  homo- 
geneous ossifying  flood. 

The  remainder  of  the  capsule  becomes,  almost  synchronously, 
transformed  into  the  periodontal  membrane. 

It  is  likely  that  a  special  cement  organ,  which  according  to 
Magitot  partakes  of  the  nature  of  fibro-cartilage,  exists  over 
the  crowns  of  the  developing  teeth  of  the  ruminating  groups 
in  Artiodactyla.  A  cement  organ,  as  such,  has  no  existence, 
however,  in  the  teeth  of  man. 

An  examination  of  the  tooth  band  of  the  permanent  tooth, 
in  Figs.  231  and  232,  would  lead  one  to  suppose  that  here  was 
a  truly  remarkable  example  of  four  successive  tooth  germs 
in  man,  viz.:  pre-milk,  deciduous,  permanent  and  post-per- 
manent (Vi,  E,  and  DP,  PZ,  and  F2).  Some  authors,  in- 


DEVELOPMENT  OF  TEETH  IN  Mammalia 


273 


FIG.   230. — To   show   the   vascular   supply   of   the   dentine   papilla.      Magnified 

55  times. 


18 


274 


DENTAL   HISTOGENESIS 


BV 


DC 


SR 


DP 


FIG.  231. — Coronal  section  through  the  mandible  of  a  human  foetus,  at  about 
the  1 70th  day  of  intra-uterine  life.  Prepared  by  decalcification,  after  fixing  in 
formic  aldehyde.  Stained  with  hsematoxylene,  and  counterstained  with  eosine. 
Magnified  15  times.  E.  Enamel  of  deciduous  tooth;  D.  Dentine;  s.R.  Stellate 
reticulum;  D.P.  Dentine  papilla;  D.C.  Dental  capsule;  p.z.  Tooth  band  of  permanent 
molar  tooth  on  lingual  side;  B.V.  Blood-vessels  extending  to  external  epithelium; 
G.  Oral  epithelium;  B.  Bone  of  jaw;  M.N.  Mandibular  nerve;  VL  A  supposed  vestig- 
ial germ  (pre-milk) ;  v2.  A  supposed  vestigial  germ  (post-permanent). 


DEVELOPMENT  OF  TEETH  IN  Mammalia 


275 


P  Z 


PIG.  232. — The  same  as  the  preceding.  To  show  the  "tufts"  on  the  tooth 
band  of  the  permanent  germ.  Magnified  75  times.  P.Z.  Tooth  band  of 
permanent  tooth  germ;  T.  "Tufts;"  Vi.  Part  of  the  tooth  band  which  might  be 
considered  by  some  authorities  to  represent  the  tooth  band  of  a  vestigial  (pre- 
milk)  tooth;  v*.  That  of  post-permanent  tooth;  B.  Blood-vessels. 


276 


DENTAL    HISTOGENESIS 


DT 


P  M 


M  N 

FIG.  233. — Sagittal  section  of  mandible  of  kitten,  with  the  deciduous  and 
permanent  teeth  in  situ.  The  former  is  fully  erupted.  Prepared  by  decalci- 
fication  after  fixing  in  formic  aldehyde,  and  hardening  in  alcohol.  Magnified 
15  times.  Represents  the  stage  of  development  in  man  about  the  i8th  month 
after  birth.  D.T.  Dentine  of  deciduous  tooth;  p.  Its  pulp;  P.M.  Blood-vessel  in 
its  root  membrane;  AO,  Its  absorbent  organ;  D,  Dentine  of  permanent  tooth; 
D.P.  Dentine  papilla  of  same;  B.  Bone  of  jaw;  G.  Gum  tissue;  M.N*.  Mandibular 
nerve. 


DEVELOPMENT  OF  TEETH  IN  Mammalia  277 

eluding  Rose,  Leche,  Kukenthal,  etc.,  would  accept  the  off- 
shoots, as  these  aberrant  tooth  bands.     As  Tomes,  however, 


B  V 


DC 


EE 


SR 


DP 


M  X 


M  A 


FIG.  234. — The  permanent  tooth  germ  of  preceding  figure.  Magnified  65 
times.  D.P.  Dentine  papilla;  o.  Odontoblasts;  D.  Dentine;  E.  Enamel;  A.  Amelo- 
blasts;  s.R.  Stellate  reticulum;  E.E.  External  epithelium;  D.C.  Dental  capsule; 
B.v.  Blood-vessels  going  down  to  external  epithelium;  D.T.  Dentine  of  deciduous 
tooth;  A.O.  Absorbent  organ  of  deciduous  tooth;  B.  Bone  of  the  jaw;  M.A.  Alan- 
dibular  artery;  M.N.  Mandibular  nerve. 


points  out  (op.  cit.  p.  352),  scepticism  can  only  be  removed  when 
these  structures  have  become  differentiated  into  external  and 
internal  epithelia,  and  calcification  is  seen  to  be  commencing. 


2y8  DENTAL   HISTOGENESIS 

(xiii)  Recapitulation 

It  seems  advisable,  for  the  simplification  of  a  somewhat 
abstruse  subject,  such  as  the  Development  of  teeth  in  Mam- 
malia, to  here  append  a  brief  outline  of  the  histories  of  the 
various  structures  met  with  during  such  a  study. 

1.  Epithelial  Inflection. — Due  to  individual  proliferation  of 
deepest  layers  of  cells  of  the  oral  epithelium,  and  collective 
penetration   into    the    sub-lying    tissues:    undergoes    cleavage 
longitudinally;    thus   forms   (i]  Labio-dental  strand  and   (ii} 
tooth  band,  Fig.  201. 

2.  Dental  Furrow. — A  slight  superficial  indentation  over  the 
epithelial  inflection. 

3.  Labio-dental    Strand,    or    Lip    Furrow. — Outer    division 
of  primary  epithelial  inflection  after  its  cleavage:  elongates  in 
vertical   direction;   widens;   central   cells    atrophy;   thus   pro- 
ducing open  sulcus  between  lips  or  cheeks  and  teeth  and  al- 
veolar processes  of  jaws,  Fig.  203. 

4.  Tooth   Band,    or   Common  Dental  Germ. — Inner  division 
of  primary  epithelial  inflection,  after  its  cleavage:  elongates: 
has  (i)  as  one  portion,  on  labial  side,  depression  which  goes 
to  form  enamel  organs  of  ten  deciduous  teeth;  and  as  another 
portion  (ii}  free  end  or  border  on  lingual  side,  which,  continuing 
to  grow,  produces  enamel  organs  of  ten  permanent  teeth  on 
lingual  side  of  deciduous  germs;  and  still  growing,   extends 
backwards  to  form  enamel  organs  of  first,  second  and  third 
permanent  molars;  is  continuous  around  whole  length  of  jaw: 
degenerates  and  becomes  cribriform;  finally  disappears,  leaving 
sometimes  small  epithelial  remnants  in  situ,  known  as  "glands" 
of  Serres,  also  epithelial  bodies  in  dental  capsule,  supernumerary 
teeth,  true  gemination,  enamel  nodules,  etc. 

5.  Enamel  Organ. — Formed  by  expansion  of  base  of  tooth 
band:  ectodermic  in  origin;  assumes  various  shapes;  consists  of 
external    epithelium,    stellate  reticulum,    stratum    intermedium 
and  internal  epithelium;  disappears  after  alveolar  crypts  are 
completed. 

6.  Neck   of  Enamel   Organ. — Attenuated    form   of   original 
tooth  band:  atrophies. 


DEVELOPMENT  OF  TEETH  IN  Mammalia 


279 


7.  External  Epithelium  of  Enamel  Organ. — Peripheral  layer 
of  round  cells  continuous  with  rete  Malpighii  on  one  hand  and 
internal    epithelium    on    other:  undergoes    modification    and 
probably  forms  cellular  layer  of  Nasmyth's  membrane. 

8.  Stellate  Reticulum. — Ectodermic  in  origin:  derived  from 
central  cells  of  tooth  band;  acts  probably  as  "packing  material" 
or  filter;  consists  of  large  stellar  cells  with  prominent  nuclei, 
and   long   branching   processes;    nuclei   atrophy  and  network 
entirely  vanishes. 


O  E 


O  E 


Z  S 


Z  P 


E  O 


FIG.  235.  FIG.  236.  FIG.  237. 

FIGS.  235,  236,  237. — Diagrams  to  show  the  tooth  band,  method  of  evolu- 
tion of  the  tooth  germs  of  the  deciduous  teeth,  and  continuation  of  the  tooth  band 
to  form  enamel  organs  of  their  permanent  successors.  O.K.  Oral  epithelium; 
T.B.  Tooth  band  in  section;  z.  Tooth  band  seen  sideways  as  a  continuous  sheet; 
E.G.  Enamel  organs;  D. p.  .Dentine  germs  of  deciduous  teeth;  z.p.  Continuation  of 
tooth  band  going  shortly  to  form  enamel  organ  of  permanent  tooth  germ  on 
lingual  side  of  the  others.  (After  Stohr.) 


g.  Stratum  Intermedium. — Layer  of  round  or  polygonal  cells 
intervening  between  last-named  tissue  and  internal  epithelium. 
from  which  it  is  separated,  according  to  Leon  Williams,  by  outer 
ameloblastic  membrane:  disappears. 

10.  Internal  Epithelium. — Continuous  at  edges  with  external 
epithelium;    forms    enamel-depositing    cells    or    ameloblasts; 
thickest  over   cusps  of   teeth   through  individual   cells   being 
longest  in  these  situations:  as  such  disappears  after  enamel  cal- 
cification is  completed,  but  most  probably  persists  in  modified 
form  as  translucent  pellicle  of  Xasmyth's  membrane. 

11.  Epithelial  Sheath  of  Hertwig. — Continuation  downwards 
to   base  of  dentine  germ  of  layer  of  internal   epithelium:  is 


28o  DENTAL    HISTOGEXESIS 

believed  to  determine  shapes  of  future  roots;  disappears;  may 
leave  unatrophied  remnants  as  epithelial  "rests"  in  periodontal 
membrane. 

12.  Dentine  Papilla. — Formed  by  upgrowth  of  mesoderm  in 
concavity  of  enamel  organ:  mesodermic  in  origin;  assumes  form 
of  future  tooth,  viz.,  conical,  premolariform,  molariform,  etc.; 
persists  as  dental  pulp. 

13.  Dentogenetic  Zone. — Band  of  formed  but  uncalcified  den- 
tine, bounded  externally  by  fully  completed  tissue,  internally  by 
layer  of  odontoblasts:  disappears  when  work  of  calcification  is 
done. 

14.  Membrana    Eboris   or  Odontoblasts. — Cylindrical  bipolar 
cells  situated  at  periphery  of  dentine  organ  and  dental  pulp; 
bounded  externally  by  dentine,  internally  by  basal  layer  of 
Weil :  perpetually  persist. 

15.  Dental  Capsule  or  Follicle. — Connective  tissue   capsule 
investing  each  tooth  germ:  mesodermic  in  origin,  whence  are 
derived  periodontal  membrane  and  cementum;  persists  till  near 
time  of  eruption,  then  atrophies. 

FORMATION    OF    THE    HARD    TISSUES 

The  study  of  the  phenomena  of  the  calcification  of  bone  and 
other  allied  tissues  involves  the  discussion  of  several  subjects, 
such  as  chemistry,  physics,  physiology,  as  well  as  histology. 
It  is  obvious  that  the  history  of  the  embryology  of  the  teeth 
would  be  incomplete  if  a  record  as  to  the  modes  by  which  osse- 
ous matter  is  deposited  in  the  soft  formative  organs  were 
omitted. 

The  histological  aspects  of  such  a  study  can  alone  be  included 
in  a  work  of  this  character:  for  the  principles  of  calcification 
generally  readers  are  referred  to  the  well-known  writings  of 
Tomes,  Sims  Woodhead,  etc. 

DEVELOPMENT   OF   THE    ENAMEL 

Sir  John  Tomes  and  his  son,  Andrews,  Leon  Williams,  and 
others  have  paid  much  attention  to  investigating  this  difficult 


DEVELOPMENT  OF  TEETH  IN  Mammalia 


281 


question:  and  it  may  be  repeated  here  that  the  absolute  truth  of 
the  matter  is  unknown:  but  the  balance  of  favour  rests  with 
those  who  hold  the  secretion  theory. 

The  following  are  brief  outlines  of  various  theories: — 
Sir  John  Tomes  considered  that  the  enamel  is  formed  by 
conversion  of  the  ameloblasts.  The  pronounced  extremities 
of  these  cells  undergo,  first  of  all,  certain  chemical  changes; 
later  on  calcification  ensues.  The  central  portions  of  the  cyto- 
plasm of  the  cells  calcify  later  than  the  peripheral:  contiguous 
cells  become  united  as  calcification  proceeds. 


I 


FIG.  238. 


FIG.  239. 


FIG.   238. — Ameloblasts,  with  Tomes'  processes. 


FIG.  240 
(After  John  Tomes  ) 


FiG.  239. — Ameloblasts,  two  of  which  have  been  immersed  in  glycerine,   and 
present  trumpet-shaped  ends  towards  the  enamel.      (After  Tomes.) 

FiG.   240. — Ameloblasts,    showing  globular   bodies,    Tomes'    processes,    and    the 
spongioplasm  of  the  cells.      (After  Tomes.) 

Charles  Tomes,  in  his  recent  researches  on  the  development 
of  enamel  in  marsupials,  is  led  to  the  following  conclusions: — 
(i)  The  ameloblast  itself  does  not  become  calcified, 
(ii)  The  chemical  and  calcareous  changes  take  place  in  or 
around  a  fibrillar  process  (Tomes'  process),  which,  being 
continuous  with  the  cytoplasm  of  the  ameloblast,  serves 
for  the  entire  length  of  an  enamel  rod,  and  solidifies 
equally  throughout  in  the  enamel  of  man  and  all  animals 
but  marsupials  and  certain  others  (see  p.  96). 
(iii)  A   tubular  condition   of   the  enamel   rods  is  probably 
merely  a  stage  through  which  all  rods  pass  during  their 
histogenesis. 


282 


DENTAL   HISTOGENESIS 


Graf  Spec1  was  the  first  to  notice  and  describe  globular  masses 
of  some  kind  of  calcareous  material  enclosed  in  the  spongio- 
plasm  of  the  ameloblasts. 

Kolliker  (op.  cit.  p.  306)  conjectured  that  enamel  rods  are 
produced  by  a  secretion  by  the  cells  of  the  enamel  membrane 
which  penetrates  the  membrana  preformativa  in  a  fluid  condition, 
but  hardens  and  ossifies  beneath  it. 


FIG.  241. 


FIG.  242. 


FIG.  243. 


FIG.  244. 


FIG.  241. — Ameloblasts  prior  to  the  start  of  formation  of  the  enamel.     (After 

Walkhoff.) 

FIG.  242. — The  same,  with  commencement  of  formation  of  the  enamel.     (After 

Walkhoff.) 

FIG.  243. — An  ameloblast.     (After  Waldeyer.) 

FIG.  244. — Isolated  ameloblasts.  H.  Homogeneous  mass  of  calcined  material, 
extended  from  the  cell  through  (c)  the  enamel  membrane  by  dialysis.  T.P. 
Tomes'  processes.  (After  von  Ebner.) 


Andrews  has  shown  (Trans.  World's  Columbian  Dental 
Congress,  vol.  I.,  1893)  that  there  is  a  deposition  of  droplets  or 
spherules  of  calcoglobulin  formed  in  the  ameloblast,  and  that 
these  are  excreted  by  these  cells  at  their  dentinal  ends  to 
build  up  the  enamel  rods.  The  "fibres  of  Andrews"  act  as 
a  sort  of  reticulum  or  scaffolding  to  determine  the  arrange- 
ment of  the  deposition;  the  existence  of  these  fibres  being 
ultimately  blotted  out  by  the  dense  calcification  of  the  tissue. 

G.  Arnell  in  "  Zur  Kenntniss  der  Zahnbildenden  Geivebe"  in 
Retzius'  "Biologische  Untersuchungen  herausg.,"  II.,  dem- 
onstrated, as  long  ago  as  1882,  that  the  inner  ends  of  the 


"Ueber  die  ersten  Vorgange  der  Ablagerung  des  Zahnschmelzes." — Anat. 
Anzeig.,  1887. 


DEVELOPMENT  OF  TEETH  IN  Mammalia 


283 


ameloblasts  are  directly  concerned  with  the  formation  of  the 
enamel  rods,  a  finely  granular  deposit  occurring  round  these 
ends. 


FIG.  245. — Section  of  developing  tooth  of  a  calf,  at  the  commencement  of 
enamel  formation.  Magnified  1,000  times.  It  is  clearly  seen  that  the  organic 
substructure  of  enamel  and  dentine  is  formed  from  the  cytoplasm  of  the  cells. 
A.  Cytoplasmic  network  in  ameloblast;  B.  c.  D.  E.  Globular  or  spherical  patterns 
of  cytoplasm.  Radiating  lines  are  seen  to  pass  from  a  central  mass  to  a  rim 
which  bounds  the  circumference,  thus  resembling  nuclear  structure.  A  like 
appearance  is  shown  in  the  completely  formed  enamel  rods.  F.  Shows  the 
cytoplasm  of  an  ameloblast  passing  without  break  of  continuity  into  the  forming 
enamel.  (Photomicrograph  by  Leon  Williams.) 


Heitzmann  and  Bodecker  consider  that  the  ameloblasts 
"break  up"  into  "embryonal  corpuscles/'  which  afterwards 
become  calcified. 


284 


DENTAL    HISTOGENESIS 


Xavier  Sudduth  thinks  that  the  ameloblasts  excrete  the 
enamel.  He  is  more  concerned  with  the  problem  whence 
they  get  their  nutritive  supply,  and  suggests  that  the  calcium 
salts  are  stored  up  in  the  meshes  of  the  stellate  reticulum  of 
the  enamel  organ,  which  thus  furnish  material  for  the  first 
formed  layer  of  enamel. 


CD 


CD 


AB 


AB 


FIG.  246. — Section  of  mature  human  enamel  of  fine  quality.  Magnified 
3,000  times.  A.B.  Calcified  cytoplasmic  network  composed  of  very  fine  granular 
threads  of  fibres;  C.D.  Enamel  rods  built  up  of  sectional  or  globular  arrangement 
of  calcified  cytoplasm.  Radiating  granular  threads  pass  from  a  central  mass 
to  the  border  of  the  sectional  part  of  the  rod.  (Photomicrograph  by  Leon 
Williams.) 

After  this  is  laid  down,  the  enamel  organ  having  disappeared 
from  over  this  calcified  layer,  a  further  supply  of  calcium  salts 
is  provided  by  a  rich  plexus  of  capillaries  which  is  found  in 
direct  communication  with  the  ameloblasts. 


DEVELOPMENT  OF  TEETH  IN  Mammalia 


285 


Leon  Williams  holds  views  on  somewhat  similar  lines. 
According  to  him,  the  stratum  intermedium  absorbs  from  the 
capillaries  an  albumen-like  substance.  This  is  ingested  by  the 
ameloblasts,  which  transform  it  into  enamel  globules,  and  so 
form  the  rods.  Globules  are  successively  produced  within  the 
ameloblasts. 


FIG.  247. — Section  of  mature  enamel,  showing  calcified  cytoplasmic  network 
at  A.  B.  and  c.  Magnified  1,500  times.  Compare  Fig.  245.  (Photomicrograph 
by  Leon  Williams.) 

"The  cytoplasm,"  he  writes,  "of  the  ameloblasts  has  a 
fairly  uniform  structure,  which  consists  of  a  number  of  globular 
masses  of  spongioplasm  of  the  same  diameter  as  the  cell,  and 
united  longitudinally  by  somewhat  coarser  plasm-strings — 
'the  fibres  of  Andrews."  "There  are  many  indications  that 
these  enamel  globules  are  formed  by  the  nucleus  of  the  amelo- 


286  DENTAL   HISTOGENESIS 

blast;  and  they  appear  to  pass  down  the  cell  by  the  natural  proc- 
ess of  growth,  as  new  ones  are  formed  above,  to  be  finally 
shed  off  the  inner  ends  of  the  cells  on  to  the  surface  of  the  form- 
ing enamel,  where  they  become  completely  infiltrated  with  the 
albumenoid  lime-conveying  substance,  and  calcified.  Enamel 
globules  are  of  uniform  size,  and  quite  distinct  from  the 
more  transparent  and  irregularly  sized  masses  of  calco- 
globulin."  "Enamel  rods  are  manufactured  by  successive, 
rhythmical,  orderly  deposits  of  these  enamel  globules,  the 
calcoglobular  masses  fusing  and  forming  the  interprismatic 
substance." 

He  finally  further  adds  (The  Dental  Cosmos,  p.  477,  June, 
1896): — "There  are  two  distinct  products  of  the  enamel- 
forming  organ.  One  of  these  products,  from  which  the  enamel 
rods  are  built  up,  is  formed  by  the  ameloblasts,  and  is  probably 
a  direct  nuclear  formation.  In  the  enamel  cells  it  takes  the 
shape  of  globular  bodies  containing  granules,  sometimes 
arranged  with  more  or  less  order,  so  as  to  resemble  the  nucleus  of 
the  cell.  In  the  formed  enamel  rod  these  globular  bodies  are, 
more  or  less,  compressed  into  disc-like  shapes,  and  are  sometimes 
nearly,  or  quite,  melted  into  one  another.  Simultaneously 
or  alternately  with  the  deposit  of  the  globular  bodies,  a  trans- 
lucent albumen-like  appearing  substance  is  seen  passing  out 
of  the  ameloblasts.  This  substance  is  probably  taken  from  the 
blood  by  the  secreting  cells  of  the  stratum  intermedium,  and 
evidently  contains  the  mineral  matter  of  which  the  com- 
pleted enamel  consists.  As  the  globular  bodies  pass  from 
the  ameloblasts  they  are  seen  to  be  connected  by  plasmic 
strings,  which  strings  can  often  be  plainly  seen  in  the  body  of 
the  ameloblasts.  The  globular  bodies  are  often  connected 
laterally  by  strings  or  projecting  processes.  Around  the 
skeleton  thus  formed,  which  constitutes  the  real  structure  of 
enamel,  the  albumen-like  substance  flows,  supplying  the 
cement  substance,  and  probably  the  mineral  matter  for  the 
calcification  of  the  whole.  All  of  this  structure  can  be  plainly 
seen  in  mature  enamel;  but  in  normal  enamel  it  is  every- 
where completely  calcified,  and  contains  no  trace  of  organic 
matter." 


DEVELOPMENT  OF  TEETH  IN  Mammalia  287 

To  sum  up:  The  theories  may  be  classified  under  three  dis- 
tinct headings: — 

(1)  Enamel  rods  are  produced  by  conversion  or  trans- 
formation in  situ  of  the  ameloblasts   (John  Tomes, 
Waldeyer,  Kolliker,  &c.). 

(2)  Enamel  rods  are  produced  by  excretion  or  secretion, 
from    the    ameloblasts    (Charles    Tomes,    Leon    Wil- 
liams, Sudduth,  Andrews,  Schafer,  &c.). 

(3)  Enamel  rods  are  produced  by  growth  of  the  amelo- 
blasts at  the  end  next  to  the  formed  enamel,  and  the 
new  growth  in  the  younger  part  is  calcified  as  soon  as 
it  is  formed  (Schwann). 

The  established  facts  that  require  no  controversy  about  this 
intricate  matter  are  quite  clear,  and  seem  to  be  that  the  layer 
of  formed  but  uncalcified  developing  enamel  is  outside  the 
main  body  of  the  ameloblasts;  that  it  has  Tomes'  processes 
penetrating  it  at  regular  intervals;  that  it  is  produced  pari 
passu  with  the  first  layer  of  uncalcified  dentine  against  which 
it  is  applied;  that  it  is  at  first  formed  and  afterwards  calcified; 
that  it  stains  deeply  with  osmic  acid;  and  that  it  chemically 
resembles  keratin,  inasmuch  as  it  offers  great  resistance  to 
destruction  by  any  of  the  mineral  acids. 

DEVELOPMENT    OF    THE    DENTINE 

Researches  as  to  the  methods  of  formation,  calcification, 
and  the  growth  of  dentine  are  not  so  beset  with  the  innumerable 
difficulties  attending  like  investigations  with  regard  to  the 
enamel.  Though  the  first  genesis  of  this  tissue  occurs  at  a 
period  of  time  slightly  antecedent  to  that  of  enamel,  the  fact 
of  its  continuance  after  the  disappearance  of  the  enamel  organ 
is  completed,  and  the  part  it  plays  in  the  production  of  the 
roots  of  teeth,  with  or  without  persistently  growing  pulps, 
as  a  physiological  process,  make  investigation  easier.  It  must 
likewise  be  remembered  that  certain  pathological  conditions 
of  the  pulp  (q.v.)  in  which  calcareous  (dentinal)  masses  are 
developed — pulp  nodules,  adventitious  dentine,  etc. — are  of 
fairly  common  occurrence.  Added  to  this,  also,  must  be  the 


288 


DENTAL   HISTOGENESIS 


fact  that  opportunities  sometimes  arise  of  observing  the  manner 
of  growth  of  dentine  in  odontomes,  where  the  fibrous  tissue 
capsule  is  still  in  normal  anatomical  relationship  with  the  hard 
parts  (see  Chapter  XV,  Vol.  II). 

Hence  it  follows  that  recent  discoveries  have  a  tendency 
to  prove  the  fallaciousness  of  the  tenets  maintained  by  Waldeyer 
in  1870,  and  also  held  by  Boll,  Beale  and  others,  and  that,  in  a 


FIG.  248. — To  show  the  process  of  calcification  of  human  dentine.  Regularly 
arranged  tubules  traverse  the  matrix,  the  sheaths  of  Neumann  being  indistinct, 
till  they  cross  one  of  the  calcospherites  in  which  calcium  salts  are  being  deposited. 
Here  they  appear  as  black  lines.  From  a  section  in  the  possession  of  A.  W.  W. 
Baker,  of  a  tooth  erupted  at  birth. 

word,  dentine  formation  proceeds  on  somewhat  similar  lines 
to  those  which  obtain  in  intra-membranous  ossification  of  bone. 
These  lines  are  not  quite  identical,  inasmuch  as  the  so-called 
odontoblast  cells  possess  persistent  processes,  and  do  not  be- 
come encapsuled  as  is  the  fashion  with  osteoblasts. 

Since  1889  the  author  has  never  held  the  view,  which  had 
been  originally  formulated  by  Waldeyer,1   that   odontoblasts 

1  "Human  and  Comparative  Histology,"  Strieker's  "Handbook;"  Sydenham, 
Soc.,  Vol.  I.,  p.  463,  1870. 


DEVELOPMENT  OF  TEETH  IN  Mammalia  289 

form  matrix,  sheath  of  Neumann,  and  dentinal  fibril;  and 
Howard  Mummery  following  up  and  amplifying  the  work  of 
von  Ebner  in  tracing  throughout  the  pulp  a  fine  connective 
tissue  stroma  which  is  continuous  with  that  in  the  dentine 
matrix,  has  unconsciously,  perhaps,  but  none  the  less  certainly, 
corroborated  this  hypothesis. 

Thus  there  is  now  established,  with  a  probably  great  degree 
of  accuracy,  the  opinion  that  dentine  is  a  product  of  certain 
round  cells  of  the  pulp  of  an  osteoblastic  nature,  whose  func- 
tion it  is  to  abstract  lime  salts  or  carbon  dioxide,  from  the 
vessels  of  the  pulp  and  lay  down  matrix  as  a  continuous  sheet 
of  formed  material  on  the  periphery  of  that  organ.  This  is 
found  in  the  teeth  of  man,  as  well  as  fish  (vaso-dentines). 

Howard  Mummery's  paper,  Philosop.  Trans.  Royal  Soc.  of 
London,  Vol.  182,  pp.  527-545,  entitled  "Some  Points  in  the 
Structure  and  Development  of  Dentine,"  should  be  perused 
by  all  interested  in  the  matter.  Here  it  need  only  be  said  that 
his  summaries  point  to  the  opinions  that: — 

(i)  The  mode  of  development  of  hard  dentine  presents  a 
strong  analogy  to  the  development  of  bone  in 
membrane. 

(ii)  In  human  dentine  trabeculas  are  seen  shooting  inwards 
into  the  pulp  from  the  surface  of  the  forming  dentine; 
these  trabeculae  sometimes  exhibiting  "an  appearance 
as  if  stiffened  by  the  deposit  of  lime  salts  in  advance 
of  the  general  line  of  calcification,"  and  being  continu- 
ous with  the  connective  tissue  fibres  of  the  pulp, 
(iii)  The  fibres  and  trabeculae  are  covered  with  cells  which 
in  many  parts  thickly  clothe  them,  and  have  similar 
functions  to  osteoblasts.  "Smaller  cells  are  inti- 
mately associated  with  the  odontoblasts  proper,  the 
latter  cells  being  also  involved  in  the  connective 
tissue  stroma  in  continuity  with  the  dentine,  and,  ac- 
cording to  the  view  which,  under  the  circumstances, 
seems  most  reasonable,  these  cells  together  secrete  a 
material  which  calcifies  along  the  lines  of  the  odonto- 
genic  fibres"  (see  Figs.  36,  37,  38,  39,  40  and  41). 
19 


290  DENTAL   HISTOGENESIS 

Since  1892,  when  the  above  was  written,  Howard  Mummery 
has  changed  his  opinion.  In  1913  he  contributed  to  the  PJiil- 
osoph.  Trans.  Roy.  Soc.  a  paper  entitled  "On  the  Process  of 
Calcification  in  Enamel  and  Dentine,"  and  his  new  views  are 
based  on  the  assumption  of  the  innervation  of  the  dentine.  He 
does  not  consider  that  sensations  are  transmitted  through  the 
dentinal  fibrils,  and  writes  as  follows: 

"The  evidences  that  the  odontoblast  cells  are  the  principal 
active  agents  in  calcification  of  the  dentine  are,  I  venture  to 
think,  quite  as  conclusive  as  the  similar  evidences  of  the  func- 
tion of  the  ameloblasts — a  function  which  has  not  yet  been 
doubted  in  their  case. 

"As  nerve-fibres  traverse  the  dentinal  canals,  the  fibril  cannot 
be  looked  upon  as  a  transmitter  of  nervous  impulses — the  cells 
have  granular  contents,  they  lie  in  a  rich  plexus  of  blood-vessels, 
and  we  know  that  active  secretion  is  associated  with  an  in- 
creased blood  supply;  like  other  secreting  cells,  they  are  large 
and  well  differentiated  from  the  surrounding  tissue  elements, 
and  they  retain  their  full  size  and  characteristics  during  the 
actual  deposition  of  the  dentine  in  healthy  teeth. 

"The  protoplasmic  prolongation  of  the  cell  in  the  form  of  the 
dentinal  fibril  would  be  considered  to  share  in  the  functions  of 
the  cell  of  which  it  forms  a  part,  and  there  are  strong  evidences 
that  calcific  matter  is  transmitted  by  the  fibril.  The  trans- 
lucent zone  in  caries,  which  a  great  weight  of  evidence  suggests 
is  due  to  calcification  in  the  tubes,  and  the  peripheral  occlusion 
of  the  tubes  on  exposed  surfaces,  point  to  this  extension  of  the 
cell  protoplasm  being  the  channel  by  which  lime  salts  are 
conveyed  to  the  dentine. 

"If  I  am  right  in  supposing  that  the  sheath  of  Neumann 
serves  as  a  dialysing  membrane,  the  comprehension  of  the  proc- 
ess of  calcification  in  the  dentine  is  somewhat  simplified.  The 
odontoblast  cell,  either  alone  or  in  common  with  other  cells  in 
the  pulp  which  send  processes  to  the  dentine,  would  deposit 
the  gelatinous  basis  substance  in  which  calcification  takes  place 
—the  substance  which  forms  the  odontogenetic  zone— the  lime 
salts  taken  up  from  the  circulating  blood  by  the  secreting  cells 
would  be  transmitted  by  the  fibril,  and  passing  by  dialysis  into 


DEVELOPMENT  OF  TEETH  IN  Mammalia  291 

the  matrix,  lay  down  the  calcifying  material  in  the  globular 
form,  slow  diffusion  of  the  component  salts,  such  as  takes  place 
through  dialysing  membranes,  being  an  important  factor  in  the 
production  of  the  calcospherites." 


THE  GROWTH  OF  THE  DENTINE  IN  THE  RABBIT  AND  CAT 

The  following  is  a  precis  of  Aitchison  Robertson's  experi- 
ments and  observations  on  the  growth  of  dentine  in  the  per- 
manently growing  incisors  and  also  in  the  canine  teeth  of  rab- 
bits and  cats.  They  were  undertaken  to  determine  whether  this 
tissue  increased  in  size  by  interstitial  growth  or  not;  and  the 
subjoined  Tables  of  measurements  and  their  summaries  are 
exceedingly  instructive  (see  Trans.  Roy.  Soc.  Edinburgh,  Vol. 
xxxvi) . 

METHOD    OF   INVESTIGATION 

"For  the  purposes  of  this  inquiry  the  lower  incisor  teeth  of 
the  rabbit  were  chosen,  for  these  teeth  grow  from  persistent 
pulps  and  are  therefore  never  shed.  To  observe  their  condi- 
tion at  different  stages  of  growth  they  were  examined  in  (i)  a 
rabbit  newly  born;  (2)  in  a  rabbit  one  month  old;  and  (3)  in 
an  adult  animal.  These  teeth,  while  still  in  situ  in  the  lower 
jaw,  were  decalcified  and  sections  made  in  an  antero-posterior 
direction  parallel  to  their  long  axes.  The  sections  from  the 
very  centre  of  each  tooth  were  alone  used  for  measurement, 
as  they  contained  the  largest  pulp  cavity  and  went  directly 
through  the  centre  of  the  crown.  These  teeth,  as  they  are 
worn  down  in  front,  are  always  being  added  to  from  behind 
and  thus  pushed  forwards.  The  enamel  is  only  found  on  the 
anterior  and  lateral  surfaces,  and  is  always  thickest  in  the  former 
position,  where  also  the  dentine  is  harder.  Consequently, 
as  the  crown  of  the  tooth  is  worn  down,  the  anterior  part, 
being  harder,  is  not  worn  so  fast,  and  thus  the  tooth  becomes 
chisel-shaped. 


292 


DENTAL   HISTOGENESIS 
MEASUREMENTS  OF  LOWER  INCISOR  TEETH  IN  RABBITS 


Newly  born 

One  month  old 

Adult 

Total  length  of  tooth 
Greatest    length    of 

H  inch  o  .  2 
Yz  inch  0.17 

%  inch  o  .  5 
6?i20  inch  0.43 

i  J£  inch  i  .  12 
i  inch  i  .0 

Greatest  breadth  of 

}<io  inch  0.033 

J-^s  inch  o  .04 

H4  inch  0.073 

Thickness  of  dentine 
at  middle  of  tooth  . 
Greatest  thickness  of 
dentine  at  crown.  . 
Diameter  of  dentinal 
tubules  at  origin.  .  . 
Width  of  intertubu- 

Kss  inch  0.0063 
J^g  inch  0.02 
H4000  inch  0.0000416 
Jsooo  inch  0.000125 

3-42  inch  o  .024 
J-^2  inch  o  .08 
H-tooo  inch  0.0000416 
Kooo  inch  0.000165 

1Mao  inch  0.044 
5H;o  inch  o.i  2 
/^40<>o  inch  0.0000416 
Hooo  inch  0.000165 

Character  of   denti- 
nal  tubules  

Run     obliquely     in 

Wavy     course;     not 

Wavy     course;  many 

straight     lines;     no 
branches;  slightly 
wider  near  origin. 

branched. 

branches. 

The  results  of  this  table  may  be  summarized  as  follows: — 

1.  The  fact  of  the  great  increase  in  length  of  the  tooth  is 
evident,  it  being  six  times  longer  in  the  adult  than  in  the  newly 
born  rabbit. 

2.  The  pulp  cavity  increases  in  length  in  the  same  proportion. 

3.  The  width  of  the  pulp  cavity  increases  in  a  progressive 
manner. 

4.  The  thickness  of  dentine  at  the  middle  of  the  tooth  and 
also  at  the  crown  increases  nearly  six  times. 

5.  The  diameter  of  the  dentinal  tubules  at  the  proximal  end 
remains  the  same  at  each  stage  of  growth.     They  are  all  slightly 
larger  at  their  origin  and  diminish  in  calibre  very  gradually 
as  they  are  traced  outwards. 

6.  The   dentinal   tubules   become  gradually  more  wavy  in 
their  course,   and   their  lateral  branches  become  evident  in 
the  adult  tooth. 

"The  odontoblasts  form  a  complete  lining  to  the  inner  sur- 
face of  the  dentine,  and  thus  form,  as  it  were,  a  bag  enclosing 
the  pulp  and  having  its  mouth  at  the  inlet  of  the  pulp  cavity. 
Dr.  Haycraft  suggested  that  the  ring  of  odontoblasts  which 
forms  the  mouth  of  this  bag  might  fitly  be  called  the  'forma- 
tive ring,'  because  it  is  apparently  here  that  new  dentine  is 


DEVELOPMENT  OF  TEETH  IN  Mammalia  293 

constantly  being  formed.  The  new  dentine  pushes  upwards 
that  previously  formed,  which  carries  with  it  the  odontoblasts 
attached  to  its  inner  surface  by  the  dentinal  fibrils.  The 
odontoblasts  which  once  composed  the  'formative  ring'  are 
therefore  carried  up  by  the  rising  dentine,  for  as  soon  as  each 
has  deposited  a  little  dentine  at  the  extreme  base  of  the  tooth, 
it  becomes  fixed  as  a  permanent  odontoblast  and  is  after- 
wards lifted  up.  Fresh  cells  are  continually  growing  below 
those  engaged  in  the  production  of  dentine,  and  thus  the  exist- 
ence of  the  'formative  ring'  is  continued.  From  whence 
do  these  new  cells  arise?  Are  they  derived  from  odonto- 
blasts, or  are  they  derived  from  the  connective  tissue  cells 
of  the  pulp?  Dr.  Robertson  inclines  to  the  belief  that  they 
arise  from  the  pulp  cells.  'If  we  trace  the  layer  of  odonto- 
blasts, we  find  that  as  the  dentine  becomes  thinner  so  the  size 
of  the  dentine-forming  cells  decreases,  till  at  the  lower  limit 
of  the  dentine  they  are  small  spindle-shaped  cells  attached 
to  the  dentine  by  their  distal  processes.  Even  below  the 
extreme  limit  of  the  dentine  we  can  still  follow  the  line  of 
odontoblasts  downwards  as  a  layer  of  fusiform  connective 
tissue  cells,  gradually  become  smaller  till  they  fade  imper- 
ceptibly into  the  pulp  tissue.  There  is  no  line  of  demarca- 
tion between  them  and  the  ordinary  small  round  cells  of  the 

Pulp." 

"The  question  now  is,  How  are  we  to  explain  how  the  tooth 
has  increased  so  much  in  size?  There  appear  to  be  four  proc- 
esses all  at  work  at  the  same  time  in  the  growing  tooth.  These 
processes  are: 

(i)  Increase  in  length  of  the  tooth  by  an  addition  of  new 
dentine  at  the  lower  end  of  the  root.  This  addition 
more  than  compensates  for  the  loss  caused  by  the 
grinding  down  of  its  crown.  In  adult  age,  the  growth 
of  new  dentine  and  the  wearing  down  balance  one 
another,  and  the  tooth  therefore  remains  of  constant 
length. 

(ii)  Increase  in  width  of  the  tooth  by  the  gradual  widen- 
ing of  the  "formative  ring;" 
(iii)  A    slight   interstitial    increase  in  the   dentine,   causing 


294 


DENTAL   HISTOGENESIS 


the  formation  of  an  increased  amount  of  matrix  be- 
tween the  tubules.  This  interstitial  increase  appears 
only  to  occur  in  the  very  young  tooth, 
(iv)  As  the  tooth  grows,  new  layers  of  dentine  are  depos- 
ited on  the  inner  surface  of  the  already  existing  den- 
tine. This  deposit  is  probably  due  to  the  influence 
of  odontoblasts,  since  they  are  concerned  in  the  pro- 
duction of  dentine  from  the  beginning. 

"As  the  entire  tooth  is  pushed  onwards  by  the  growth  of 
new  dentine  at  its  lower  end,  the  crown  is  continually  being 
worn  down  in  grinding.  The  upper  end  of  the  pulp  cavity  is 
very  narrow  and  contracted,  owing  to  the  large  amount  of 
dentine  which  has  accumulated  on  its  surface,  for  in  this  situ- 
ation the  dentine  is  of  oldest  date  and  so  is  thickest.  Un- 
less provision  were  made  to  prevent  it,  the  pulp  cavity  would 
soon  become  exposed  by  reason  of  the  grinding  down  of  the 
crown.  It  is  here,  however,  at  the  upper  part  of  the  pulp 
cavity,  that  the  dentine  reaches  its  maximum  thickness,  and 
so  reduces  the  diameter  of  the  pulp  cavity,  that  it  persists 
only  as  a  fine  channel  of  considerable  length  leading  from 
the  pulp  cavity  to  the  free  surface  of  the  tooth.  Osseous 
tissue  is  developed  in  this  channel,  which,  together  with  many 
small  round  cells  and  capillaries,  prevents  any  direct  com- 
munication between  the  surface  of  the  tooth  and  the  pulp. 
No  odontoblasts  remain  in  this  connecting  channel;  therefore, 
since  the  dentinal  fibres  in  the  crown  of  dentine  have  lost 
their  connection  with  nerves  the  grinding  surface  of  the  rabbit's 
incisor  has  lost  sensitivity.  These  laminae  of  bone  which  help 
to  block  up  the  remains  of  the  pulp-cavity  at  the  apex  of  the 
tooth  may  be  part  of  the  layer  of  cement  which,  in  the  persist- 
ently growing  teeth  of  many  animals,  covers  over  the  crown  of 
the  tooth,  and  which  may  when  worn  away  sink  into  the  almost 
occluded  apex  of  the  pulp-cavity  and  grow  there.  It  may, 
however,  be  developed  directly  from  the  tissue  of  the  pulp. 

"In  the  adult  rabbit's  tooth,  then,  the  growth  of  dentine  at 
the  'formative  ring,'  the  continual  deposition  of  new  dentine 
on  the  inner  surface  of  the  old,  and  the  extent  to  which  the 
tooth  is  worn  down  externally,  exactly  balance  one  another, 


DEVELOPMENT  OF  TEETH  IN  Mammalia 


295 


and  thus  the  tooth  remains  of  the  same  size  throughout  life. 
In  the  young  growing  animal,  however,  the  first  two  of  these 
processes  exceeds  the  third,  and  so  the  tooth  grows  greatly 
in  length,  diameter,  and  thickness  of  dentine. 

"Having  seen  how  a  simple  conical  tooth  increases  in  size, 
the  next  question  which  naturally  arose  was,  How  do  flask- 
shaped  teeth,  such  as  the  canine  tooth  of  a  cat,  increase  in  size? 
To  answer  that  question,  the  canine  tooth  of  the  lower  jaw 
was  examined  in  (i)  a  newly  born  kitten;  (ii)  in  a  kitten  of 
one  month  old;  and  (iii)  in  the  adult  cat.  These  teeth  in 
the  cat,  as  in  all  Carnivora,  are  shed  at  an  early  period  of  ex- 
istence. This  introduces  a  slight  fallacy,  for  it  compels  one 
to  compare  deciduous  with  permanent  teeth. 

MEASUREMENTS  OF  LOWER  CANINE  TEETH  IN  CATS 


Newly  born 

One  month  old 

Adult 

Total  length  of  tooth  .  . 

Ys  inch  0.196 

18%oo  inch  0.366 

59ioo  inch  0.59 

Greatest  length  of  pulp 

cavity 

5^5  o  inch  o  .  1  8 

^&  5  inch  0.32 

/•2  inch  o  .  5 

Greatest    breadth    of 

pulp  cavity  

^"125  inch  0.056 

^J^oo  inch  0.074 

^£5  inch  o  .04 

Thickness    of   dentine 

at  middle  of  tooth  .  .  . 

J'izoo  inch  o  .006 

x250  inch  o  .036 

'/io  inch  o  .06 

Greatest    thickness  of 

dentine  at  crown.  .  .  . 

Ko  inch  0.0166 

2  Hoo  inch  o  .046 

•Koo  inch  o  .09 

Diameter   of   dentinal 

tubules  at  origin  

MTOOO  inch  0.0000589 

HTOOO  inch  0.0000589 

at  base  M2000  inch 

0.0000833 

at  crown  /•£  7  o  o  o  inch 

o  .000037 

Width   of  intertubular 

dentine  

K250  inch  0.000235 

^4250  inch  0.000235 

at  base  ^4250  inch 

0.000235 

at  crown  /^ooo  inch 

o  .000166 

This  table  shows  that  (i)  The  lower  canine  tooth  of  the 
adult  cat  is  fully  three  times  as  long  as  it  is  in  the  newly 
born  kitten. 

(ii)  The  pulp  cavity  grows  longer  in  the  same  propor- 
tion. 

(iii)  As  regards  the  width  of  the  pulp  cavity,  it  seems  first 
to  increase  in  breadth,  but  in  the  adult  tooth  the  breadth 
is  less  than  in  the  newly  born  kitten. 


2g6  DENTAL    HISTOGENESIS 

(iv)  At  the  middle  of  the  tooth  the  dentine  increases  to  a 
thickness  ten  times  greater  than  in  the  newly  born 
kitten;  while  at  the  crown  it  increases  to  about  six  times. 
(v)  The  diameter  of  the  dentinal  tubules  was  the  same 
in  the  young  kittens.  In  the  adult  cat,  however, 
the  tubules  at  the  base  of  the  tooth  are  one-half  larger 
than  those  of  the  younger  cats;  but  near  the  crown 
their  diameter  decreases  greatly,  being  a  half  less  than 
in  the  younger  cats,  and  even  two-and-a-half  times 
smaller  than  at  the  base  of  the  same  adult  tooth. 
(vi)  The  width  of  the  intertubular  substance  remains  the 
same  in  the  canines  of  kittens  and  also  at  the  base  of 
the  adult  tooth.  At  the  crown  of  the  adult  tooth, 
however,  it  is  only  three-fourths  of  the  breadth  of  what 
it  is  at  the  root,  or  in  the  younger  teeth. 

"Before  describing  how  this  tooth  grows,  particular  atten- 
tion must  first  be  directed  to  a  fact  on  which  the  importance  of 
this  inquiry  rests,  viz.,  this,  that  the  canine  tooth  of  young 
kittens  is  not  flask-shaped,  but  merely  conical,  resembling 
the  extinguisher  of  a  candle,  the  sides  sloping  downwards  and 
outwards  from  the  crown.  This  originally  conical  tooth  in- 
creases in  size  as  follows: 

1.  By  the  gradual  dilatation  of  the  'formative  ring'  of  cells 
at  the  base  of  the  dentine  it  is  increased  in  diameter. 

2.  It  is  increased  in  length  by  the  addition  of  new  dentine 
at  the  base  of  the  tooth  and  the  consequent  elevation  of  the 
whole  tooth.     This  also  is  due  to  the  action  of  the  formative 
ring. 

"These  two  processes  go  on  simultaneously,  and  so  the  base 
of  the  tooth  is  always  growing  larger  while  the  tooth  is  grow- 
ing in  length.  This  outward  extension  of  the  basal  formative 
ring  of  odontoblasts  goes  on  till  a  maximum  is  reached.  This 
broadest  part  of  the  pulp  in  the  growing  tooth  of  the  kitten 
is  at  the  base,  while  in  the  adult  cat  it  remains  about  the  middle 
of  the  tooth.  Thus  in  the  newly  born  kitten  the  broadest 
diameter  of  the  pulp  cavity  was  at  the  base  of  the  conical 
tooth,  and  measured  0.056  inch.  In  the  kitten  one  month  old, 
the  basal  diameter  of  the  pulp  was  still  the  greatest,  the  tooth 


DEVELOPMENT  OF  TEETH  IN  Mammalia  297 

still  being  conical,  and  measured  0.074  inch.  It  had  not  yet 
become  flask-shaped,  but  about  this  time  the  pulp  cavity  attains 
its  greatest  breadth  and  afterwards  diminishes.  The  elongation 
of  the  tooth  still  continues,  but  the  formative  ring  now  gradually 
contracts,  and  thus  forms  an  inverted  basal  cone  and  so  leads 
to  the  production  of  the  flask.  The  narrowing  of  this  basal  ring 
continues  until,  in  the  adult,  it  becomes  a  small  ring  surrounding 
the  vessels  and  nerves  going  to  the  pulp.  The  elongation  of 
the  tooth  has  also  caused  its  broadest  part  to  be  situated  about 
midway  between  crown  and  base.  Thus  the  tooth  is  made  up 
of  two  cones  joined  at  their  bases,  the  'crown-cone'  being 
formed  by  a  dilatation  of  the  'formative  ring'  and  the  'root-cone' 
by  the  gradual  narrowing  of  the  ring. 

"3.  During  the  whole  time  that  the  tooth  is  growing  in 
length,  a  constant  deposition  of  new  dentine  is  taking  place 
on  the  inner  surface  of  the  old.  Thus  the  maximum  diameter 
of  the  pulp  cavity  in  the  young  tooth  becomes  lessened,  till, 
in  the  adult,  the  original  pulp  cavity  is  much  reduced  in  size 
compared  with  its  width  in  the  newly  born  kitten.  Having 
reached  this  stage  the  processes  of  growth  cease,  and  thus  a 
typical  flask-shaped  tooth  is  produced.  We  see  now  how  the 
apparent  anomaly  regarding  the  width  of  the  pulp  cavity 
arises.  From  the  table  we  find  that  the  width  of  this  cavity 
is  less  in  the  adult  tooth  than  it  is  in  the  new-born  kitten. 
This  is  due  to  the  large  deposit  of  new  dentine  on  the  inner 
surface  of  the  old,  causing  such  a  narrowing  of  the  pulp  cavity 
that  the  above  condition  is  produced. 

"4.  It  is  also  shown  that  there  has  been  an  interstitial 
change.  The  dentinal  tubules  are  smaller  and  closer  together 
near  the  crown  of  the  adult  tooth  than  near  the  base.  At  the 
base  the  amount  of  intertubular  dentine  remains  the  same  as 
it  is  in  the  younger  cat's  tooth,  though  the  tubules  themselves 
are  a  good  deal  larger  in  diameter  than  in  the  earlier  conditions. 

"  Regarding  root-formation,  we  have  seen  how  a  single 
rooted  tooth,  as  the  canine,  is  developed  by  the  gradual  nar- 
rowing of  the  basal  dentine-forming  ring.  If,  however,  this 
formative  ring,  having  reached  its  maximum  dilatation,  be- 
comes constricted  at  two  opposite  points  till  these  meet  like  a 


298  DENTAL   HISTOGENESIS 

figure-of-eight,  then  two  smaller  formative  rings  are  produced. 
If  these  both  go  on  forming  dentine  and  diverging  from  one 
another,  we  have  two  'root-cones'  produced,  springing  from  one 
body  and  giving  us  a  double  rooted  tooth.  In  a  similar  manner, 
if  the  formative  ring  becomes  sub-divided  into  three  or  four 
rings,  we  have  a  three  or  four  rooted  tooth  resulting.  The  tooth 
capsules  themselves,  even  of  the  molar  teeth,  are  quite  simple 
and  show  no  indication  of  roots.  It  is  only  after  the  body  of 
the  tooth  has  been  completed  that  the  roots  are  produced. 
"This  inquiry  shews  that  the  growth  of  a  tooth  is  only  to  a 
very  slight  extent  interstitial.  Interstitial  growth  is  seen  in 
the  incisor  tooth  of  the  rabbit,  where  the  dentinal  tubules 
become  further  separated  by  an  increase  of  dentinal  matrix, 
but  this  appears  to  take  place  only  in  the  young  tooth.  Prob- 
ably it  causes  a  slight  increase  in  the  size  of  the  rabbit's 
tooth.  In  the  cat,  however,  it  does  not  cause  any  increase  in 
the  size  of  the  tooth;  the  width  of  the  intertubular  substance 
remains  the  same.  It  is  only  in  the  upper  part  of  the  adult 
tooth  that  the  tubules  are  smaller  and  more  closely  packed. 
All  we  can  affirm  in  this  case  is  that  the  interstitial  increase 
of  the  matrix  simply  encroaches  on  the  size  of  the  tubules 
and  so  does  not  cause  any  increase  in  the  size  of  the  tooth. 

EXAMINATION    OF    THE    TEETH    OF    YOUNG    RABBITS 
FED    ON    MADDER 

While  working  at  this  subject  Professor  Haycraft  gave 
Dr.  Robertson  the  teeth  of  three  young  rabbits  which  had 
been  fed  on  madder  for  a  fortnight.  He  carefully  examined 
these,  as  he  thought  they  might  throw  some  light  on  the  mode 
of  growth  in  teeth. 

I.  The  first  rabbit  was  killed  after  being  fed  on  madder 
for  two  weeks.  All  the  stained  part  of  the  tooth  is  that  pro- 
duced while  the  madder  was  added  to  the  food.  In  the  section, 
this  staining  reached  the  very  crown  of  the  tooth,  but  only  at 
the  centre.  This  clearly  demonstrates  that  there  is  a  constant 
deposit  of  new  dentine  on  the  inner  surface  of  the  old.  At  the 
apex  of  the  pulp  cavity  the  colour  is  deepest,  for  most  of  the 


DEVELOPMENT  OF  TEETH  IN  Mammalia  299 

new  dentine  was  deposited  in  that  situation.  It  is  also,  seen 
that  there  is  a  narrow  band  of  stained  dentine  which  immediately 
surrounds  the  pulp.  These  teeth  also  shew  that  the  incisor 
teeth  increase  in  length  much  more  rapidly  than  the  others; 
for,  while  the  incisor  is  stained  in  three-fourths  of  its  length, 
the  premolar  is  stained  in  only  half  its  length. 

II.  The  second  rabbit  was  fed  for  two  weeks  on  madder, 
and  then  on  ordinary  food  for  a  similar  period.     The  lower 
part  of  the  incisor  tooth,  and  also  a  narrow  strip  of  dentine 
surrounding  the  pulp  cavity  and  extending  up  to  the  grinding 
surface,  is  now  unstained.     This  is  all  new  dentine,  formed 
during  the  'last  two  weeks  of  the  animal's  life.     In  the  pre- 
molar the  axial  staining  is  hardly  yet  worn  away.     The  deeper 
staining  of  the  dentine  on  the  concavity  of  the  incisor  may  be 
due  to  the  more  rapid  growth  which  there  is  in  this  situation, 
and  the  greater  consequent  absorption  of  the  circulating  stain. 

III.  The  third  rabbit  was  also  fed  on  madder  for  two  weeks, 
then  on  ordinary  food  for  three  weeks.     The  teeth  shew  merely 
a  further  development  of  what  No.  II.  did.     These  madder- 
stained  teeth  corroborate  entirely  the  explanation  of  the  growth 
of  the  dentine  which  has  been  already  given. 

The  results  of  this  investigation  into  the  growth  of  teeth  may 
be  thus  summarised.  There  is: 

1.  Increase  in  the  length  of  the  tooth  by  addition  of  new 
dentine  at  its  base; 

2.  Increase  of  diameter  by  dilatation  of  the  basal  formative 
ring.     In  the  case  of  teeth  with  roots,  these  are  produced  by 
the   gradual   contraction   of   this   ring   with   or   without   sub- 
division ; 

3.  Deposit  of  new  dentine  on  the  inner  surface  of  the  old; 

4.  A  slight  increase  in  the  matrix  of  the  dentine  by  interstitial 
growth. 

THE    GROWTH    OF    THE    INCISOR   TEETH    OF    THE    ALBINO    RAT 

This  has  been  carefully  studied  by  Drs.  W.  H.  F.  Addison, 
and  J.  L.  Appleton,  Jr.,  of  the  University  of  Pennsylvania, 
Philadelphia,  who  in  an  elaborate  paper,  "The  Structure  and 


300 


DENTAL   HISTOGENESIS 


Growth  of  the  Incisor  Teeth  of  the  Albino  Rat,"  Journal  of 
Morphology,  Vol.  26,  1915,  have  arrived  at  the  following  con- 
clusions : 

"The  rate  of  growth  of  the  upper  and  lower  incisor  teeth 
of  Mus  norvegicus  albinus,  in  the  mature  animal,  averages  2.2 
and  2.8  mm.  per  week,  or  12.5  cm.  and  14.5  cm.  per  year, 
respectively. 

"Growth  is  due  primarily  to  the  proliferation  and  growth 
of  cells  at  the  basal  end  of  the  enamel-organ,  where  new  enamel- 
forming  cells  arise,  and  at  the  basal  end  of  the  dental  papilla 
where  new  dentine-forming  cells  develop. 

"The  enamel-organ  of  the  adult  forms  a  narrow  circular  band 
around  the  basal  end  of  the  tooth,  and  extends  forward  from 
this  on  the  labial  side  only.  It  coincides  in  its  lateral  bound- 
aries with  the  enamel,  and  extends  along  the  entire  imbedded 
portion  of  the  tooth.  Anteriorly,  it  comes  in  contact  with  the 
epithelium  of  the  gingival  margin,  and  is  carried  out  continually 
as  a  narrow  band  of  cells  lying  on  the  enamel,  between  the 
latter  and  the  gingival  epithelial  tissue. 

"The  first  indication  of  the  tooth  band  of  the  incisors  appears 
in  i4-day-old  foetuses.  In  foetuses  21  days  of  age  (just  before 
birth),  enamel  and  dentine  formation  is  beginning.  In  animals 
i  day  old  the  upper  and  lower  teeth  measure  2.3  and  3  mm. 
At  8  to  10  days  the  teeth  erupt,  and  at  10  days  measure  7  and 
ii  mm.  respectively.  This  period  is  therefore  characterised  by 
the  rapid  elongation  of  the  teeth. 

"The  process  of  attrition  begins  within  a  few  days  after  erup- 
tion, so  that  by  19  or  21  days  of  age,  the  typical  occlusal  surface 
is  formed.  Up  to  the  time  of  eruption  the  anterior  end  or  apex 
of  the  tooth  is  immediately  under  the  oral  epithelium,  while 
the  basal  or  growing  end  is  continually  progressing  posteriorly. 
After  eruption,  the  basal  end  becomes  nearly  stationary  in 
position,  while  the  whole  tooth  structure  is  continually  moving 
forward.  The  extra-gingival  length  of  the  tooth  is  kept  con- 
stant, however,  by  the  attrition  of  the  occlusal  surface,  either 
through  use  in  gnawing  or  by  the  action  of  the  opposing  teeth. 

"The  histogenesis  of  the  enamel-organ  is  practically  com- 
pleted by  the  fourth  day  after  birth,  although  it  does  not  attain 


DEVELOPMENT  OF  TEETH  IN  Mammalia  301 

its  final  relations  to  the  tooth  as  a  whole,  until  after  eruption. 
In  the  1 8-day  foetus  the  enamel-organ  is  similar  in  all  parts, 
and  the  cells  of  the  inner  layer  measure  the  same,  both  lingually 
and  labially.  From  this  period  forwards,  however,  the  labial 
portion  continues  to  progress  towards  its  fully  differentiated 
functional  structure,  while  the  lingual  portion  retrogresses,  un- 
til at  4  days  after  birth  the  latter  is  disrupted,  by  the  ingrowth 
of  the  surrounding  connective  tissue.  Contrasting  the  cells  of 
the  inner  layer — the  potential  ameloblasts — on  the  labial  and 
lingual  sides,  they  are  practically  the  same  in  the  1 8-day  foetus, 
but  at  19  days  they  are  found  to  measure  24  and  20  /x  respec- 
tively. In  the  2 1 -day  foetus,  they  measure  30  to  34  and  12  /z, 
and  i  day  after  birth  the  true  ameloblasts  on  the  labial  side 
have  increased  to  40  /z,  while  the  non-functional  cells  of  the 
lingual  side  are  only  10  /z  in  height.  At  4  days,  the  latter  cease 
to  form  a  continuous  layer,  by  reason  of  the  dispersion  of  the 
cells  by  the  surrounding  connective  tissue,  except  at  the  basal 
formative  region. 

"Characteristic  of  the  permanently-growing  enamel-organ 
are  the  epithelial  papillae,  formed  by  the  elevations  of  the  outer 
layer  of  the  enamel-organ,  and  the  cells  of  the  enamel  pulp. 
Between  these  elevations  are  numerous  capillaries  which  insure 
a  rich  blood  supply  to  the  enamel-forming  cells. 

"There  are  three  layers  in  the  functional  enamel-organ — 
inner,  middle  and  outer.  The  inner  is  constituted  of  the  tall 
ameloblasts,  and  the  middle  is  made  up  of  two  divisions,  (a) 
stratum  intermedium  and  (b)  enamel  pulp.  The  latter  unites 
with  the  single  layer  of  cuboidal  cells  which  compose  the  outer 
layer,  to  form  the  epithelial  papillae. 

"The  apex  of  the  primitive  tooth  is  formed  of  a  variety  of 
secondary  dentine — 'osteo-dentine'  of  Tomes — which  is  softer 
than  true  dentine,  and  differs  in  its  structural  arrangement. 
After  eruption,  this  terminal  portion  of  osteo-dentine  is  soon 
worn  away  by  attrition,  and  the  typical  occlusal  surface  is 
developed,  as  seen  at  19  or  21  days.  At  21  and  23  days  the 
first  two  molars  erupt  in  both  upper  and  lower  jaws,  and  from 
now  on,  the  animal  is  able  to  secure  food  for  itself,  and  if 
necessary  can  maintain  an  independent  existence. 


302 

"As  the  tooth  continues  to  be  worn  away  there  is  a  provision 
for  the  continual  filling  in  of  the  apex  of  the  pulp-chamber  by 
the  formation  of  what  may  also  be  called  osteo-dentine.  This 
is  a  form  of  secondary  dentine,  containing,  when  first  formed, 
cells  and  blood-vessels.  This  is  always  at  a  little  distance, 
about  i  mm.,  from  the  occlusal  surface,  but  as  any  part  of  the 
tooth,  in  its  outward  progression  approaches  the  occlusal  sur- 
face, the  soft  elements  disappear  within  the  osteo-dentine,  and 
the  latter  forms  a  hard  continuous  surface  with  the  adjoining 
true  dentine.  The  position  of  this  osteo-dentine  is  marked  as 
a  line  on  the  occlusal  surface  of  the  teeth. 

"Prior  to  eruption  there  develops  around  the  apex  of  the 
tooth,  as  it  lies  in  contact  with  the  surface  epithelium,  a  thick- 
ened ring  of  stratified  epithelium.  This  ring  of  tissue  is  pierced 
by  the  apex  (i.e.,  cutting  or  incisive  edge)  of  the  tooth  at  erup- 
tion, and  would  seem  to  have  the  function  of  serving  as  a 
resistant  margin  for  the  soft  tissues,  and  of  preventing  other 
tissues  being  carried  along  with  the  erupting  tooth. 

"The  length  of  the  teeth  varies  with  the  size  of  the  cranium, 
so  that  the  persistent  growth  is  not  only  sufficient  to  offset  the 
continual  attrition,  but  also  serves  to  keep  the  length  of  the 
teeth  in  a  definite  relation  to  the  length  of  the  skull,  as  the 
latter  increases  in  size. 

"The  lower  tooth  is  always  longer  than  the  upper,  and  this 
difference  manifests  itself  even  in  the  tooth-bands  of  these 
structures  in  the  ig-day  foetus. 

DEVELOPMENT   OF   THE    CEMENTUM 

Of  this  there  need  be  but  little  said;  mere  repetition  of 
descriptions  of  phenomena  which  are  probably  now  under- 
stood with  the  greatest  certainty,  is  needless.  Suffice  it  to 
say,  that  there  is  every  reason  to  believe  that  cementum  is 
developed  ordinarily  after  the  manner  of  intramembranous 
ossification  of  bone.  Where  thick  layers  of  the  tissue  exist 
over  the  crowns  of  teeth,  Magitot's  opinion  that  develop- 
ment and  ossification  in  a  cement  organ  of  fibro-cartilagmous 
character  is  most  probably  accurate. 


DEVELOPMENT  OF  TEETH  IN  Mammalia 


3°3 


THE    STAGES    OF  DEVELOPMENT   OF   THE   JAWS   AND    TEETH   IN   A 
HUMAN   EMBRYO    OF   HALF-TERM 

For  the  purpose  of  investigation,  and  in  order  to  put  on 
record  a  careful  account  of  the  degrees  of  development  arrived 
at,  at  a  certain  period  of  growth,  the  right  half  of  the  upper 
jaw  of  a  human  foetus  of  about  20  to  25  weeks  was  employed. 


FIG.  249. — To  show  an  early  stage  in  calcification  of  cementum.  Magnified 
500  times.  A.  Granular  layer  of  Tomes  partly  calcified;  B.  Young  cementum. 
(Photomicrograph  by  Norman  Broomell.) 


This  was  apparently  absolutely  normal,  and,  as  far  as  could 
be  ascertained,  believed  to  be  unaffected  by  rachitis,  syphilis,  etc. 
The  jaw  was  subdivided  into  seven  sections,  beginning  at 
the  front,  in  a  sagittal,  and  behind,  in  a  coronal  direction,  and 
included  the  following  regions,  enclosing  deciduous  teeth: — i, 
first  incisor;  2,  second  incisor;  3,  canine;  4,  anterior  molar; 
5  and  6,  posterior  molar,  and  7,  behind  the  posterior  molar, 
near  the  maxillary  tuberosity.  The  latter  showed  no  dental 


3°4 


DENTAL   HISTOGENESIS 


FIG.  250. — From  region  of  first  maxillary  deciduous  incisor.  Magnified 
30  times.  For  description  of  this  and  following  figures,  see  Tables  A.  and  B. 
on  pp.  306  and  307. 


DEVELOPMENT  OF  TEETH  IN  Mammalia 


305 


structures  whatsoever.     The  figures  at  the  heads  of  the  fol- 
lowing columns  indicate  these  various  regions  (see  pp.  306  and 

3°7). 

Carefully  decalcified  and  embedded  in  paraffin,  the  tissue 
was  cut  serially,  and  typical  mesial  vertical  sections  selected 


E?P 


PZ 


FIG.  251. — From  region  of  second  incisor  as  in  preceding  figure.  Magnified 
30  times.  P.Z.  Permanent  tooth  germ;  E.P.  Epithelial  "Pearl"  or  "  Gland  of 
Serres." 


for  pictorially  and  verbally  illustrating  the  phases  of  devel- 
opment. It  will  be  observed  that  in  consequence  of  the  action 
of  reagents  some  shrinkage  of  the  embryonic  dentine  germ  has 
taken  place.  To  prevent  tautology,  brief  tables  only  need  here 
be  introduced. 


THE    HISTOGENESIS    OF    OVARIAN    TEETH 

Not  much  is  known  as  to  the  development  of  those  anoma- 
lous misshapen  dental  structures  found  in  the  oophoronic  cysts 
of  the  human  ovary.  Sir  John  Bland-Sutton  has,  however,  ex- 


306 


DENTAL   HISTOGENESIS 


o 

ft 

•"  o 

0 

II 

•d 
o 

J3 

•eg 

M    C 

c  ft 

ft 

c 

'rt  g 

"2  i 

"3 

0 

rt 

•"  o 

s 

g"a 

•d 

•d 

C 

°"rt 

^ 

0^2 

c 

ui 

>, 

O 

n 
o 

o 
c 
o 

1 

o 

rt  o 

t:  > 

M 
g 

HH 

B 
O 

^"o  o 

o 
•d 

1—1 

c 

o 

C 

rt 

Pi 

c 

rt 

o 
"3 

'o  ^ 

bo 

^•^3-C 

C-£ 

jjj 

i/i 

18  rt  ° 

13 

5  2, 

rt 

in 

o 

2^3  -u 

2 

OJ 

tc 

X> 

rt 

^"S^ 

£ 

B 

•d 

•3  § 

rt  g: 

+a 

..  O  § 

o 

rt 

o 

-f^ 

^  o 

o 
o 

E 

GJ    O    C 
—  ^    rt 

c 

p 

g 

(H 

rt 

•2 

o 

C 
O 

o 

5  rt 

•z 

£ 

£    ° 

^ 

- 

i—  i 

^ 

^ 

2; 

2- 

5-1 

•d-fi 

T  ""^ 

o 

08  § 

•^  o"rt    . 

.S 

-0  *j 

0  S  3  !? 

"t4  C 

rC    -tJ 

S  S  o  rt 

og 

*->  C 

o  o^J 

IP 

i 

i 

1 

» 

a 

c 

t 

_  a 

^t" 

c3  "^ 

-C              yj  T^ 

1 

rt 

.£  rt 

P 

i 

lig'S 

'g  >-       ft 

i 

5 
i 

'   s 

•d 

I 

o 

2  ft  S 

^30^ 

1 

! 

rt 

^M-t 

•* 

£ 

M 

V 

< 

,  —  -^ 

i 

^"o  bo 

rt  c  2  o 

£  *  B-d 

C 

f  •* 

O 

m 

^r 

rt 

s 

01 

H 

M 

Spear-like  point. 

Slender  cap. 

Broad:  discontinuous 
at  base  of  tooth  germ. 
Tooth  band  of  per- 
manent tooth  germ 
bulbous. 

Triangular  with 
smaller  triangle  over 
apex:  very  embry- 
onic constituents. 

T 
' 
( 

! 

' 

C 

j 
) 
j 

3 

2 

3 

LI 

Broad:  large  amount. 

Cubical  cells,  continu- 
ous with  dental  cap- 
sule at  base  of  tooth 
germ:  small  epithe- 
lial "tufts"  appear. 

M 

Differentiated  into 
outer  and  inner 
parts. 

Greatly  developed  a- 
way  from  oral  sur- 
face: very  wide 
gutter. 

M 

Thick  investment: 
reaches  nearly  to 
base  of  dentine. 

Thick  cap  over  apex. 

Narrow:  tooth  band 
of  permanent  tooth 
germ  just  discerni- 
ble. 

Triangular  in  shape: 
vessels  assuming 
usual  characteristics. 

i 

) 

J 

3 

3 

3 

U| 

-  —  . 

Discontinuous  a- 
round  toojth  germ. 

Discontinuous. 

'o 

u 

rt 

.0 

u 

rt 
o 

C 

£  S 
«-° 

Differentiated. 

Thick:  several  layers; 
gutter  widely  open. 

•d«  g 

*"  rt'o  — 
c  c.     "d 

•d 
c 

O   "  O 

.g 

>d 

c 

•gi 

o  rt  o 

S  "s-o 

Ill's 

3 
O 

a 

K 

i 

3 

!^ 

3 
O 
IH 

rt 

•d 

p,"o 

o 
-3_>. 

M 

\\\ 

u£M 

CJ  -^    C 
>  C   3"d 

3  S' 

O    0 

3  bo 

:ii 

) 
) 

5 

3'S 

°a 

c"o 

ii 

3  M 

•d 

0 

4* 

a 
C 

'd  o 

C 

"^  "  fe    ' 

•o^  <«  «*H 

•s-S 

_S  >,:=T3 

3 

4J    O 

•£•£ 

o 
^ 

2 

<o 

T—I  *-• 

•p  o  g  c 
P  6*d+3 

i  nil 

c  "o 

0  O 

o*- 

J^gl 

(. 

H 
'       ^ 

C    rt 

0^3 

0 

c"o 

o  o 
U~ 

rt 

s 

ig 

Q 

O  4J       . 

.     3-d 
^  be  o 

g 

B 

;2 

o 

rt 

J 

o 

N 

0) 

§ 

rt 
bo 

'5. 
rt 

» 

tn 

'_> 

'ft 

CJ 

O 

"3 
a 

O 

o 

ft 

.3 

^3 

0 

(3 

rt 

>, 

"3 

0 

•Jj 

o 

o 

0 

"si 

o 
be 

rt 

g 

•J 

g 

•jj 

0 

rt 

C 

O 

rt 

2 

rt 
C 

a 

o 
Q 

rt 
c 
W 

C 
0 

3 
E 

E 
•d 
O 

"3 

0 
X 

w 

c 
Q 

C 
0 

Q 

M 

rt 

DEVELOPMENT  OF  TEETH  IN  Mammalia 


3°7 


S  "E  ° 

a  a 
a  a  o 

o 

M        O 

0     10 

O      O    t*J      £j     IO 

10 

O 

0 

^3  '£    p  ,cS 

5 
Z 

o 
Z 

p  •§  £   S 

"o  -5  "3 

0    ^     ° 

a  ^ 

IO 

IO 

0     I- 

ro   « 

0    I? 

o   o  ^   ^ 

10 

n 

j 

o 

c 
o 
Z 

o 
o 
Z 

S"  Jj     £     g 

t 

O    t- 

10 

10 

r-    O 

10 

o   o 

O      M 

HI         IO 

O     10 

PI 

HI      00 

t~    O 

O     O 

05 

10 

o   o 

o   o 

0     10 

<3  °  — 

00      N 

o 

o 

o   -> 

O     M    5 

.SP 

HI 

O     N 

N 

X     l~ 

0 

O    M 

O        M 

-^     p-l 

o 
u 

SC  "S 

—  5 

e 

o 

£  -2    : 

thickness, 
extent.  .  .  . 

thickness, 
extent  .  .  . 

&  ^ 

II 

l-l 

«  1  * 

3  5 

<A   ^ 

r3 

c 

\ 

T    u   ^j 

— 

—-' 

'£• 

o 

£ 

"•3  s  1 

"3 

rt 

c 

w 

C 

0 

Q 

Dentine 

Enamel 

o 

>  '-3    a 

3o8 


DENTAL   HISTOGENESIS 


FIG.  252. — From  region  of  canine,  as  in  preceding  figure.     Magnified  30  times. 


DEVELOPMENT  OF  TEETH  IN  Mammalia  309 


E  P 


FIG.   253. — From  region  of  deciduous  first   molar,   as  in  preceding  figure. 
Magnified   15  times.     E.P.  Epithelial  "Pearl"  or  "Gland  of  Serres." 


FIG.   254. —  From    region    of    deciduous    second   molar,    as    in    preceding    figure. 

Magnified  15  times. 


3io 


DENTAL   HISTOGEXESIS 


PlG.  255. — From  posterior  portion  of  region  of  deciduous  second  molar  as  in 
preceding  figure.     Magnified  10  times. 


DEVELOPMENT  or  TEETH  IN  Mammalia 


311 


amined  many  specimens.  These  are  fully  described  in  his 
"Tumours,  Innocent  and  Malignant,"  1906.  The  accom- 
panying Fig.  256,  taken  by  permission  from  his  work,  shows 


EO 


f?   DP 


FlG.  256. — Composite  drawing  of  the  microscopical  appearances  in  a  teratomat- 
ous  cyst  of  the  ovary.  E.O.  Enamel  organ;  D.P.  Dentine  papilla;  E.P.  Epithelial 
pearl . 


the  component  parts  in  the  formation  of  a  tooth.  Cf.  the 
"Epithelial  Pearl"  (E.P.),  with  the  same  bodies  in  Figs.  251 
and  253.  These  are  regarded  by  Bland-Sutton  as  enamel 
organs. 


CHAPTER  XIII 

DEVELOPMENT  OF  THE  TEETH  IN  PISCES,  REPTILIA  ] 
AND  BATRACHIA 

MICROSCOPICAL  ELEMENTS  IN:  Developing  Teeth  of  (i)  Cod;  (ii)  Dog- 
fish; (iii)  Crocodile;  (iv)  Lizard;  (v)  Snake;  and  (vi)  Newt. 


In  Pisces 

Fishes  are  vertebrate  animals  which  live  in  water,  and  breathe  the  air 
dissolved  in  the  water  by  means  of  gills  or  branchiae.     The  two-chambered 
heart  consists  of  a  ventricle  and  auricle  or  atrium.     The  limbs,  excepting 
in  the  Cyclostomata  and  Leptocardii  (which  are  apodal),  are  modified  into 
fins,   supplemented  by  unpaired  median  fins.     The  skin  is  either  naked, 
scaly,  or  covered  with  osseous  plates.     Fishes,  as  a  rule,  are  oviparous. 
The  class  of  Fishes  is  divided  into  the  following:1 — - 
Sub-class  I.  Elasmobranchii. 
Order  i.  Proselachii. 
Order  2.  Acanthodides. 
Order  3.  Selachii. 

Sub-order  i.  Xotidani. 
Sub-order  2.  Squali. 
Sub-order  3.  Raii. 

Order  4.  Pleuracanthodes  (  =  Ichthyotomi). 
Sub-class  II.  Holocephali. 
Sub-class  III.  Ostracodermi. 
Order  i.  Heterostraci. 
Order  2.  Osteostraci. 

Order  3.  Pterichthyomorphi  (  =  Antiarcha). 
Sub-class  IV.  Dipnoi. 

Order  i.  Ctenodipterini. 

Order  2.  Monopneumones. 

Order  3.  Dipneumones. 

Order  4.  Coccosteomorphi  (  =  Arthrodira). 

1  This  is  the  classification  adopted  (1908)  by  Sir  E.  Ray  Lankester  and  Dr. 
Ridewood  of  the  British  Museum  (Natural  History  Department). 

312 


DEVELOPMENT    OF    TEETH    IN   PlSCCS  313 

Sub-class  V.  Teleostomi. 

Order  i.  Stylopterygii*  (  =  Crossopterygii,  auct.). 
Sub-order  i.  Tarrasioides  (  =  Haplistia). 
Sub-order  2.  Holoptychioides  (=  Rhipidistia). 
Sub -order  3.   Ccelacanthoides  (  =  Actinistia). 
Sub-order  4.  Polypteroides  (  =  Cladistia). 
Order  2.  Astylopterygii.* 

Sub-order  i.  Sturioniformes  (  — Chondrostei). 
Sub-order  2.  Amiiformes  (  =  Protospondyli). 
Sub-order  3.  Lepidosteiformes  (  =  /Etheospondyli). 
Order  3.  Neichthyes  (  =  Teleostei). 
Grade  A.  Physostomi. 

Sub-order  i.  Salmoni-clupeiformes  (  =  Isospondyli). 
Sub-order  2.   Cyprini-siluriformes  (  =  Ostariophysi). 
Sub-order  3.  Symbranchiformes. 
Sub-order  4.  Anguilliformes  (  =  Apodes). 
Sub-order  5.  Esociformes  (  =  Haplomi). 
Grade  B.  Physoclisti. 

Sub-order  6.  Halosauriformes  (  =  Heteromi). 
Sub-order  7. — Gastrosteiformes  (  =  Catosteomi). 

Division  i.  Selenichthyes. 

Division  2.  Hemibranchii. 

Division  3.  Lophobranchii. 

Division  4.  Hypostomides. 
Sub-order  8.  Mugiliformes  (  =  Percesoces). 
Sub-order  9.  Gadiformes  ( =  Anacanthini,  in  part). 
Sub-order  10.  Acanthopterygii. 

Division  i.   Perciformes. 

Division  2.  Scombriformes. 

Division  3.  Zeorhombiformes. 

Division  4.  Kurtiformes. 

Division  5.  Gobiiformes. 

Division  6.   Echeneiformes  (  =  Discocephali). 

Division  7.  Trigliformes  (  =  Scleroparei). 

Division  8.  Blenniiformes  (  =  Jugulares). 

Division  9.  Trachypteriformes  (  =  Taeniosomi). 

Division  10.  Mastacembeliformes  (  =  0pisthomi). 
Sub-order  n.  Lophiiformes  (  =  Pediculati). 
Sub-order  12.  Balistiformes  ( =  Plectogriathi) . 

It  is  unnecessary,  in  a  work  of  this  character,  to  give  more 
than  a  brief  outline  of  the  manner  in  which  the  teeth  of  Fishes 
are   evolved.     The   simplicity   of   the   process   is   remarkable 
*  These  are  often  spoken  of  as  "Ganoid  Fishes." 


DENTAL   HISTOGENESIS 

and  of  interest,  especially  when  the  development  and  succession 
of  teeth  in  Mammalia  have  been  studied. 

Two  examples  need  only  be  here  detailed. 

One  occurs  in  the  Teleostomi,  the  other  in  the  Elasmobranchii. 

In  Teleostomi 

Example. — Order — Neichthyes.  Sub-order — Gadiformes,  in 
the  division  Gadidae  (Cod-fishes). 

The  simplest  arrangements  of  parts  are  well  exhibited  in 
the  jaws  of  young  Cod-fishes  of  about  10  cm.  body  length. 
Gadus  luscus  may  be  taken  as  a  type. 

Under  low  powers  the  oral  epithelium  is  very  remarkable 
for  its  depth  and  strength;  its  thickness  may  exceed  that  of 
the  sub-mucous  tissue.  The  free  surface  is  somewhat  thrown 
into  wrinkles  or  folds.  The  deeper  layer  of  cells  is  of  the 
usual  columnar  shape.  The  submucous  tissue  extends  into  the 
former  in  the  shape  of  many  narrow  numerous  papillae. 

The  tooth  germs,  originating  de  novo,  are  developed  in  the 
tissue  which  fills  a  papilla,  which,  with  the  growth  of  the  germ, 
becomes  widened  and  flattened. 

Minute  Structure  of  Tooth  Germ.- — There  is  no  tooth  band  and 
no  heaping  up  of  epithelium.  An  ill-constituted  enamel  organ 
exists,  the  stellate  reticulum  of  which  is  of  a  rudimentary  char- 
acter, consisting  merely  of  strands  of  fibres;  no  cells  and  no 
nuclei  fill  the  inter-spaces.  The  ameloblasts  are  short  cylinders 
with  large  oval  nuclei  separated  from  a  well-defined  stratum 
intermedium  by  a  clear  narrow  zone. 

The  odontoblasts  are  prominent.  At  the  base  of  the  den- 
tine germ,  the  mesodermic  cells  about  to  form  the  pulp  are 
sharply  differentiated  from  the  underlying  structures,  and  no 
dental  capsule,  as  such,  occurs.  The  odontoblasts  of  mature 
teeth  are  rounded  or  flattened,  adhering  closely  to  the  dentine, 
and  in  a  striking  way  resembling  osteoblasts.  They  are  not 
distinguishable  from  the  pulp  cells  in  any  other  particular  than 
their  position.  These  same  cells  in  younger  teeth  shew  tran- 
sitional changes  from  these  round  forms  to  long  cylindrical 
cells,  whose  nuclei  are  not  particularly  marked. 


DEVELOPMENT    OF    TEETH   IN  Pisces 


315 


In  the  Gadidce  (e.g.,  Gadus  Marrkud)  Rose1  describes  the 
odontoblasts  as  extraordinarily  long  and  thin  cells  in  the 
young  tooth  rudiments.  But  Fig.  3,  which  accompanies  his 
paper,  shews  the  cells  to  be  longest  and  thinnest  over  the 
deepest  base  of  the  dentine,  and  gradually  diminishing  in 
length  and  width  as  they  approach  the  cutting  edge. 

In  every  section  of  Gadus  luscus  prepared  by  the  author 
this  is  not  the  case.  The  cells  half-way  down  the  young  tooth 


o  E/ 


Y  T 


O  T 


FIG.  257. — Vertical  section  through  jaw  of  a  young  cod  fish.  Prepared  by 
hardening  and  decalcification.  Stained  with  Ehrlich's  acid  hcematoxylene. 
Magnified  50  times,  o.x.  Oldest  tooth  germ;  o.  Odontoblasts,  in  several  layers, 
at  base  of  tooth ;  Y.T.  Youngest  tooth  germ;  O.E.  Oral  epithelium;  B.  Bone  of  the 
jaw. 

germs  are  the  largest,  those  at  the  oral  edge  and  at  the  base 
smaller  and  rounder,  till  at  the  extreme  limit  of  the  develop- 
ing pulp,  they  are  flat  and  scale-like  and  adherent  to  the  den- 
tine. Inspection  of  the  photomicrograph,  however,  at  first 
sight  would  seem  to  indicate  that  Rose's  description  is  correct. 

1  "  On  the  Various  Alterations  of  the  Hard  Tissues  in  the  Lower  Vertebrate 
Animals."  Translated  from  the  Anatomischer  Anzeiger,  in  the  Journal  Brit. 
Dent.  Assoc.,  Jan.,  1899. 


316  DENTAL    HISTOGEXESIS 

But  the  appearances  here  produced  are  due  to  several  layers 
of  small  cells,  which  become  curiously  congregated  in  this 
way.  The  chief  point  is  that  the  nuclei  are  in  no  sense  of  the 
word  increased  or  elongated. 

In  structure  the  dentine  is  vitro-dentine,  according  to  Rose. 
(For  the  meaning  of  this  term  see  p.  108).  In  the  cases  just 
noted  it  (the  dentine)  possesses  no  canals,  scanty  tubes,  but 
faint  laminations.  The  tooth  germs  move  in  an  outward 
direction,  and  when  fully  completed  are  found  perched  on  the 
pedestal  of  bone  known  as  the  "bone  of  attachment." 


In  Elasmobranchii 

Example. — Order — Selachii;  sub-order — Squall;  family — 
Scylliidce  (Dogfish) . 

Specimens  of  Scyllium  caniculum  afford  excellent  types  of 
the  genesis,  evolution  and  eruption  of  the  teeth. 

The  epithelium  of  the  mouth  is  not  flat,  as  in  Mammalia, 
but  is  beset  with  myriads  of  elevations  of  microscopic  size. 

The  outermost  layers  are  not  particularly  cornified. 

At  varying  distances  there  occur  on  the  outer  surface  of  the 
lip,  the  dermal  spines,  each  of  which  is  imbedded  by  means  of  a 
widened  broad  base  in  the  submucous  tissue.  In  some  places 
their  close  association  causes  these  spines  to  become  imbricated. 

The  accompanying  photomicrograph  shews  the  remarkable 
analogy  between  the  teeth  and  these  placoid  scales  or  dermal 
denticles.  In  fact,  the  latter  may  all  be  considered  modified 
teeth,  differing  chiefly  in  function  and  positions  (see  Fig.  258). 

In  addition  to  the  variation  in  their  positions,  these  spines 
are  modified  in  regard  to  shape,  size,  and  structure. 

In  form,  the  greater  number  which  cover  the  surface  of  the 
skin  of  the  animal  are  flattened  plates,  with  a  slightly  convex 
free  margin,  and  wedge-shaped  bases  securely  dovetailed 
into  the  firm  dermal  connective  tissue. 

On  the  edge  of  the  jaw  the  exposed  portion  becomes  rounded 
and  presents  a  fungiform  outline,  while  at  the  place  of  inflexion 
over  the  jaw  margin  it  assumes  the  appearance  of  the  flattened 


DEVELOPMENT    OF    TEETH   IN  PlSCeS 


317 


LZ 


FIG.  258. — Vertical  section  through  the  jaw  of  a  young  dogfish.  Prepared 
by  hardening  and  decalcification.  Stained  with  borax-carmine  and  Ehrlich's 
acid  haematoxylene.  The  vertical  lines  are  markings  made  by  a  dull  razor 
during  cutting  on  an  ether-freezing  microtome.  Magnified  25  times,  c.  Carti- 
lage of  the  jaw,  with  semi-ossified  external  crust;  D.E.  Epithelium  of  the  skin; 
O.E.  Epithelium  of  the  mouth;  L.Z.  Lowest  extent  of  the  tooth  band;  D.P.  Dentine 
papilla  of  young  tooth  germ;  F.T.  Functional  tooth;  s.  Two  teeth  about  to  be  shed; 
P.S.  Pulp  tissue  in  centre  of  a  dermal  denticle.  A.  Aperture  at  base  of  dermal 
denticle  for  passage  of  blood-vessels  to  the  pulp. 


318  DENTAL    HISTOGEXESIS 

head  and  beak  of  a  bird.  In  size,  the  latter  are  by  far  the 
larger. 

In  structure,  each  denticle,  similarly  to  each  dental  organ, 
possesses  a  central  pulp  chamber,  filled  with  abundant  round 
cells  and  a  fairly  well  organised  blood  system.  The  hard 
parts  contain  dentinal  tubes,  which  radiate  in  the  usual  way. 

The  epithelium  of  the  mouth  is  considerably  deeper  than 
that  of  the  skin,  and  extends  almost  to  the  base  of  each  tooth; 
for  here,  at  the  oral  border,  the  denticles  become  teeth  in  func- 
tion, being  merely  transitional  in  structure.  It  embraces  the 
teeth  very  intimately.  An  aperture  at  the  side  of  the  base 
admits  the  passage  of  blood-vessels  to  the  pulp. 

The  tooth  band  is  continuously  growing,  and  dips  down 
deeply  as  far  as  the  curved  recess  of  the  cartilaginous  frame- 
work of  the  jaw.  Here,  as  in  the  deepest  locality,  are  the 
youngest  teeth  germs.  This  tooth  band  is  of  great  thickness, 
and  is  highly  specialised.  It  extends  as  a  broad  column  down 
the  side  of  the  jaw  cartilage,  and  in  it  are  the  developing  teeth. 

In  the  dogfish  the  deepest  layer  of  the  tooth  band  produces 
the  ameloblasts  as  in  other  creatures;  and  the  next  deepest  layer 
of  cells  forms  what  must  be  analogous  with  the  stratum  inter- 
medium of  mammalian  enamel  organs. 

Throughout,  the  deepest  layer  is  composed  of  long  cylin- 
drical cells  closely  packed  together,  containing  oval  or  flattened 
granular  nuclei.  The  external  layer  is  very  short  and  the  nuclei 
are  correspondingly  abbreviated. 

By  counter-staining,  the  young  teeth  may  reveal  what  is 
probably  a  thin  superficial  band  of  enamel. 

The  dentine  and  the  pulps  of  the  teeth  are  developed  from 
the  connective  tissue.  The  cells  in  the  situation  of  the  future 
dentine  papilla  become  approximated,  and  in  the  pulps,  while 
still  retaining  their  rounded  forms,  can  be  easily  seen  to  deposit 
ossific  material  on  the  sides  of  the  connective  tissue  scaffolding 
of  the  dentine. 

In  the  interspaces  of  the  developing  teeth,  the  deepest  layer 
is  arranged  like  a  loop. 

Thus,  enamel  organs  as  highly  specialised  as  in  Mammalia, 
are  non-existent  and  no  dental  capsules  surround  the  papillae. 


DEVELOPMENT    OF    TEETH    IN   Reptilid  319 

II 

In  Reptilia 

The  class  of  Reptiles  is  divided  into  the  following  orders: — i.,  Crocodilia; 
ii.,  Rhynchocephalia;  iii.,  Lacertilia;  iv.,  Ophidia;  and  v.,  Chelonia. 
In  i.  (Crocodile,  Garial,  Alligator)  the  teeth  are  implanted  in  sockets; 
in  ii.  (New  Zealand  Lizard  or  Sphenodon  punctatus)  they  are  anky- 
losed  to  the  summits  of  the  jaws,  the  bone  at  their  bases  undergoing  a 
secondary  upgrowth  (hyperacrodont),1  but  are  soon  lost  by  attrition, 
their  functions  being  carried  on  by  the  dense  free  margins  of  the 
maxilla  and  mandible;  in  iii.  (Lizards)  they  are  ankylosed  and  non- 
socketed;  and  in  iv.  (Snakes)  the  same;  while  in  v.  (Turtles  and 
Tortoises)  they  are  absent . 

In  Crocodilia 

The  genesis  of  the  teeth  in  Crocodiles  resembles  in  a  marked 
degree  that  of  mammalian  animals.  An  exhaustive  descrip- 
tion would  be,  in  the  main,  little  better  than  a  mere  recapitula- 
tion of  the  story.  Suffice  it  to  say  that  the  teeth  succeed  ver- 
tically, being  thecodont — i.e.,  contained  in  the  same  socket. 
Absorption  of  the  functional  tooth  by  its  successor  takes  place, 
owing,  no  doubt,  to  some  form  of  absorbent  organ,  as  in  man. 
It  is  interesting  to  compare  photomicrographs  of  these  two 
conditions.  (See  Figs.  233  and  259). 

In  Lacertilia 

The  common  English  Green  Lizard  (L.  viridis)  may  be 
employed  as  a  type. 

The  chief  characteristics  are  the  great  length  of  the  tooth 
band,  and  the  consequent  depth  of  the  enamel  organ  and  dentine 
germ.  As  far  as  the  maxilla  is  concerned,  the  whole  tooth 
.germ  is  placed  as  closely  as  possible  to  a  concavity  in  the  upper 
and  inner  surface  of  the  jaw  at  the  base  of  the  functional  tooth. 

The  ameloblasts  are  considerably  elongated,  and  extend 
deeply  down  the  sides  of  the  dentine  germ.  The  layer  is 
continuous,  as  in  man,  with  the  external  epithelium.  There 

1  See  paper  by  Howe  and  Swinnerton  on  "The  Development  of  the  Skeleton 
of  the  Tuatera."  Trans.  Zoological  Soc.,  Feb.,  1901. 


320 


DENTAL    HISTOGENESIS 


D  S 


FIG.  259. — Vertical  section  of  mandible  of  young  crocodile.  Prepared  by 
hardening  and  decalcification.  Stained  with  borax-carmine  and  Ehrlich's  acid 
haematoxylene.  Magnified  20  times.  D.F.  Dentine  of  functional  tooth;  D.S. 
Dentine  of  successional  tooth;  B.  Bone  of  jaw;  M.  Mucous  gland. 


DEVELOPMENT    OF    TEETH    IN    Reptilid 


321 


is  no  stellate  reticulum  in  the  otherwise  well-differentiated 
enamel  organ,  but  the  intermediate  space  is  occupied  by  a 
few  cells  with  elongated  nuclei.  Apparently  no  cells  analo- 
gous to  the  stratum  intermedium  exist. 

The  continuation  of  the  tooth  band  is  in  a  line  with  the 
deep  part  of  the  external  epithelium  of  the  enamel  organ  of 


DP 


OE 


C  Z 


DPS 


FIG.  260. — Vertical  section  of  jaw  of  an  acrodont  lizard.  Prepared  as  in 
preceding  figure.  Magnified  25  times.  D.F.  Dentine  of  functional  tooth;  D.P.S. 
Dentine  papilla  of  successional  tooth  germ;  O.E.  Oral  epithelium;  c.z.  Continu- 
ously growing  tooth  band;  B.  Bone  of  jaw  to  which  the  functional  tooth  is 
ankylosed;  M.  Mucous  gland. 


the  neighbouring  young  tooth  germs,  and  in  direct  conti- 
nuity with  the  deepest  layer  of  cells  of  the  original  tooth 
band. 

The  dentine  germ  is  made  up  of  a  dense  mass  of  oval  cells, 
which  at  the  periphery  are  somewhat  elongated. 

The  submucous  tissue  by  condensation  of  its  cells  and 
fibrous  tissue  produces  an  "adventitious  capsule." 


322 


DENTAL    HISTOGEXESIS 


In  Opliidia 


The  bone  of  the  jaw  of  the  common  or  Ringed  Snake  (Tro- 
pidonotus  natrix)  is  somewhat  pyriform,  with  a  broad  flat- 
tened base.  The  functional  tooth  surmounts  this.  Occu- 
pying a  site  internal  to  the  bone,  the  young  tooth  germs  are 
found  very  closely  placed,  not  only  to  one  another,  but  to 
the  body  of  the  bone  itself. 


O  E 


FIG.  261. — Vertical  section  of  jaw  of  snake.  Prepared  as  in  preceding  figure. 
Stained  with  Ehrlich's  acid  hsematoxylene.  DI.  Dentine  of  oldest  tooth  germ; 
O.  Odontoblasts  of  the  dentine  papilla  of  the  same;  D>.  Dentine  of  next  oldest 
tooth  germ;  DS.  04.  05.  Dentine  of  younger  tooth  germs;  De.  Dentine  of  youngest 
tooth  germ;  B.  Bone  of  jaw;  O.E.  Oral  epithelium;  M.  Muscle  fibres. 


Typical  sections  shew  the  oldest  tooth  germs  to  be  triangular 
in  outline,  while  the  developing  teeth  in  vertical  sections 
have,  as  a  rule,  a  circular  shape.  The  oldest  of  the  develop- 
ing teeth  in  some  sections  presents  a  V-shaped  outline.  This 
apparent  morphological  difference  is  due  to  the  fact  that  the 
circular  teeth  are  cut  transversely,  and  the  others  obliquely, 
lying  as  they  do  in  a  recumbent  or  semi-recumbent  position 
before  they  assume  the  erect  attitude. 


DEVELOPMENT    OF    TEETH    IX    Bdtrachid  32.3 

The  great  part  of  the  tooth  is  composed  of  ortho-dentine. 
The  layer  of  odontoblasts  is  of  interest,  inasmuch  as  the  cells 
near  the  base  are  the  most  elongated  of  all,  those  at  the  incisive 
margin  being  small  and  round.  The  tooth  band  is  very  short, 
surrounding  each  germ.  It  is  of  continuous  growth. 

The  oral  epithelium  differs  in  a  curious  fashion  from  that  of 
other  reptiles.  Here  it  consists  of  long,  narrow  cells,  which 
have  almost  the  appearance  of  ciliated  columnar  cells.  There 
is  only  one  layer,  and  it  is  arranged  on  a  sort  of  basement 
membrane,  which  is  puckered  up  into  folds  after  the  fashion 
of  the  fungiform  papilla?  of  the  tongue. 

Ill 

In  Balrachia  (Frogs  and  Newts) 

These  animals  are  cold-blooded  vertebrates,  which  for  some,  or  the  whole, 
period  of  their  existence  breathe  by  gills,  and  in  adult  life  from  lungs. 
The  heart  is  tri-lobed,  having  two  ventricle  and  one  auricle.  Some  are 
ecaudate  and  apodal.  The  larva  is  fish-like  and  breathes  by  means  of 
gills,  which  later  on  are  replaced  by  lungs.  Some,  however,  retain 
their  gills,  while  certain  frogs  leave  the  egg  in  a  perfect  form.  They 
may  be  oviparous  and  ovoviviparous. 

They  are  divided  into  the  following  orders: 

(i)    Ecandata  —  Frogs  and  Toads,  the  former  of  which  is  edentulous   as 

far  as  the  lower  jaw  is  concerned,  the  latter,  as  to  both  jaws. 
(ii)    Caudata  —  Xewts,  Salamanders,  &c. 
(iii)  Apoda,  or  Ccecilians. 


The  plate  and  mandibular  bones  of  the  newt  (Molge  i~ul- 
garis)  are  extremely  thin  and  delicate.  In  the  median  line. 
at  its  innermost  margin,  the  palate  bones  are  thickest,  the 
intervening  portions  being  of  remarkable  tenuity. 

Development  of  the  teeth  begins  in  the  oral  epithelium 
which  is  near  the  free  margins  of  the  bone,  by  a  down-growth 
of  epithelium.  The  tooth  band  is  shallow,  but  very  flat, 
and  grows  continuously  towards  the  middle  line. 

The  oral  epithelium  possesses  several  characteristics. 

The  cells  are  exceedingly  brilliant,  being  almost  transparent 
in  nature,  that  is,  the  cytoplasm  is  scarcely  granular.  This 


324 


DENTAL   HISTOGENESIS 


O  E 


makes  the  large  oval  nuclei  particularly  prominent,  and  helps, 
too,    to  reveal  the  karyoplasm  and  chromatin  they  contain. 
The  phenomena  of  mitosis  may  be  well  studied  here.     The 
epithelial  layer  is  almost  twelve  cells  deep.     There  is  no  cel- 
lular differentiation  into  a  rete  Malphigii. 

The  constituents  of  the  tooth  band  are  flattened  bodies  with 
flat  nuclei,  and  they  lie  more  or  less  in  a  direction  which  is 
parallel  to  the  palate. 


FIG.  262. — Coronal  section  of  the  head  of  a  newt,  with  the  mandible  detached 
and  removed.  Prepared  similarly  to  the  preceding  figure.  Magnified  15  times. 
O.K.  Oral  epithelium;  F.T.  Functional  tooth;  E.G.  Enamel  organ  of  young  tooth 
germ,  the  tooth  band  being  continued  beyond  it  towards  the  centre  of  the 
palate;  N.F.  Nasal  fossa. 

In  a  typical  tooth  germ  which  is  beginning  to  assume  a  defi- 
nite shape,  the  dentine  organ  is  occupied  by  an  assemblage 
of  large  elongated  cells  with  reticular  nuclei.  The  dentine 
is  formed  at  a  very  early  period  of  growth. 

Outside  this  hard  tissue  is  a  layer  of  smaller  rounder  cells, 
and  outside  this  is  a  second  layer,  separated  from  the  former 
by  a  clear  translucent  line  or  space. 


DEVELOPMENT    OF    ATYPAL    DENTINES  325 

There  is  hardly  any  attempt  at  the  formation  of  an  enamel 
organ;  if  it  exists  at  all,  it  is  an  exceedingly  rudimentary 
structure. 

In  the  anterior  part  of  the  mouth,  the  two  inwardly  ex- 
tending tooth  bands  of  the  palate  meet  and  become  fused,  and 
form  a  continuous  uninterrupted  sheet  of  epithelium,  cut  off  on 
the  outer  side  from  the  oral  epithelium,  by  a  thin  band  of 
submucous  tissue,  whose  characteristics  are  small  narrow 
cells  imbedded  in  a  clear  matrix  scantily  supplied  with  fibres, 
and  forming  a  succession  of  young  teeth  placed  side  by  side 
on  the  thin  jaw  bone.  The  youngest  tooth  germs  are  in  the 
centre  of  this  band,  the  oldest  at  its  margin. 

DEVELOPMENT    OF  VASO-   AND   PLICI-DENTINE 

The  process  of  development  is  essentially  the  same  as  that 
described  in  connection  with  hard  or  orthodentine  (q.v.  p.  287). 

It  is,  however,  somewhat  modified  by  the  fact  that  the 
odontoblasts  are  of  rounded  shape  like  osteoblasts  (Tomes), 
which  deposit  calcine  material  along  the  bundles  of  connec- 
tive tissue  fibres,  which  in  the  case  of  fishes  are  most  pro- 
nounced on  the  surface  of  the  pulp.  The  capillaries  remain  in 
situ,  and  the  dentine  is  deposited  around  them,  leaving  channels 
in  the  dentine. 

With  regard  to  plici-dentine,  the  mode  of  formation  is  iden- 
tical, but  the  capillaries  are  not  conserved  in  the  dentine. 

In  Carcharias,  as  Tomes  has  pointed  out,  the  organic  matrix 
of  the  outer  layer  (probably  enamel)  is  furnished  by  a  special- 
ized layer  of  the  dentine  papilla,  and  over  this  are  ameloblasts 
of  enormous  length.  They  may  measure  JQ/J.  or  SO/JL. 

DEVELOPMENT    OF    OSTEO-DENTINE 

The  surface  of  the  pulp  is  first  ossified  in  the  usual  way,  by 
deposition  of  lime  salts  around  its  odontogenic  fibres.  Thus 
the  outer  sheath  of  hard  dentine  is  manufactured. 

The  bulk  of  the  tissue  is,  however,  developed  after  the 
manner  of  intra-membranous  ossification  of  bone;  that  is, 


326  DENTAL  HISTOGEXESIS 

rods  of  osseous  material  run  through  the  long  axis  of  the  pulp, 
being  continuous  externally  with  the  rest  of  the  great  fas- 
ciculi of  connective  tissue  fibres  which  freely  traverse  the 
central  soft  organ.  As  Tomes  says  (op.  cit.  p.  202):  "Osteo- 
blasts  clothe,  like  an  epithelium,  the  trabeculas  and  the  con- 
nective tissue  fibres  attached  to  them,  and  by  the  calcification 
of  these  the  osteo-dentine  is  formed." 


APPENDIX 
NOTE  A 

ON  THE  FUNCTIONS  OF  THE  CELLS  OF  THE  PULP 

I 

The  questions  relative  to  the  functions  and  uses  of  the 
odontoblasts  are  deep  and  intricate,  and  for  years  have  been 
the  subject  of  earnest  inquiry.  Many  theories  as  to  their 
properties  have  been  brought  forward. 

It  will  be  helpful,  for  a  clear  comprehension  of  what  is  to 
follow,  to  briefly  enumerate  these  various  opinions.  Tomes,1 
and  with  him  the  majority  of  observers,  once  believed  in  (A)  the 
conversion  theory  of  the  formation  of  dentine.  The  cells 
undergo  changes  and  become  converted  into  matrix,  sheath 
and  fibril.  In  recent  years,  however,  Tomes  has  spoken  on 
this  point  with  no  slight  degree  of  uncertainty.  In  1893,  he 
remarked,2  "We  have  always  been  accustomed  to  say  that 
they  (the  odontoblasts)  formed  the  whole  of  the  dentine;  now 
we  know  that  they  do  not." 

Further,  Walkhoff3  expresses  his  opinion  that  the  dentine 
processes  serve  essentially  for  the  nutrition  of  the  dentine, 
the  forms  of  the  odontoblasts  being  in  complete  accord  with 
their  functional  requirements.  ("Ihre  Formen  passen  sich  den 
jeweiligen  Funktionsbediirfnissen  durchaus  an.") 

Again,  many  histologists  including  Magi  tot,  Kolliker,  etc., 
hold  to  (B)  the  secretion  theory,  maintaining  that  the  dentinal 
matrix  is  secreted  from  these  cells. 

1  "Dental  Anatomy,"  p.  170,  1889. 

2  Jour,  of  Brit.  Dent.  Assoc.,  vol.  xiv.,  p.  474. 

5  "Die  Normale  Histologie  Menschlicher  Zahne,"  p.  128,  1901. 

327 


328  APPENDIX 

Klein1  subscribed  to  the  belief  that  the  odontoblasts  form 
matrix  only,  while  the  fibrils  are  not  their  processes,  but  stretch 
out  from  a  deeper  layer  of  cells.  In  addition,  there  is  the 
theory  of  Heitzmann  and  Bodecker,  apparently  corroborated 
by  Abbot  of  New  York.2  Here  the  odontoblasts  are  said 
to  be  first  broken  up  into  "medullary  corpuscles"  at  their 
distal  end,  which  become  infiltrated  first  with  a  glue-yielding 
basis  substance,  and  afterwards  with  lime-salts.  Thus  many 
conflicting  views  exist. 

The  axiom  that  dentinal  fibrils  are  considered  to  be  sensa- 
tion conductors  is  well  known  to  all.  Inasmuch,  then,  as 
they  are  regarded  functionally  in  the  light  of  nerves,  and  as 
they  represent  the  peripheral  poles  of  the  odontoblasts,  and 
are,  in  fact,  part  and  parcel  of  those  cells,  it  follows  that  the 
latter  must  be  concerned  in  the  act  of  conveying  extrinsic 
stimuli  to  the  nerves  of  the  pulp.  An  odontoblast  is  more  of 
a  sensation  transmitter  than  a  sensation  generator.  In  other 
words,  it  is  believed  to  be  a  means  of  communication  between 
fibril  and  nerve  telodendria — not  originating,  but  passing  on  sen- 
sory impulses  from  without  in,  and  warning  the  pulp,  so  to 
speak,  of  incoming  dangers.  This  seems  to  the  author  a 
sensible  argument,  and  this  is  his  theory. 

In  order  to  prove  this,  it  is  necessary  to  show  (i)  that  odon- 
toblasts do  not  form  dentine,  as  is  generally  understood; 
(2)  to  prove  that  they  are  the  end  organs  of  the  nerve  filaments 
of  the  pulp. 

Negative  Evidences 

The  arguments  to  disprove  the  dentine-forming  theory  are 
many  and  important.  They  are  as  follow: 

i.  No  observer  has  ever  seen  a  semi-calcified  odontoblast, 
or  recorded  the  observation  of  one  secreting  a  calcareous  ma- 
terial, although  this  has  been  done  over  and  over  again  with 
regard  to  the  ameloblasts  of  the  enamel  organ,  as  Tomes3 
and  Leon  Williams  have  demonstrated. 

1  "Atlas  of  Histology,"  p.  185,  1880. 

2  Dental  Cosmos,  Sept.,  p.  821,  1893. 

3  Op.  cit. 


APPENDIX  329 

2.  The  same  cell  cannot  take  on  two  totally  different  func- 
tions    simultaneously.     In     general     normal     histology    it    is 
found  that  complex,  branched,  ganglionic  bodies  exist  in  the 
nervous    system,    while    very    simple    cells — osteoblasts — pro- 
duce the  matrix  of  bone.     There  must  be  a  separate  cell  for  the 
formation  of  fibril  and  matrix. 

3.  The  presence  of  spaces  between  odontoblasts  would  lead 
one  to  expect  to  find  like  spaces  in  dentine,  but  this  is  not  so. 
Per  contra,  active  osteoblasts  are  closely  packed  together. 

4.  As  fibrils  and   their   sheaths   are  known  to  cross  inter- 
globular  spaces,  and  as  the  latter  are  considered  to  be  an  arrest 
of  dentinal  development,  one  would  expect  that  if  the  fibrils 
were   formed   by   the   same   agents   as  those  which  produced 
matrix,  they  themselves  (fibrils)  would  be  absent;  but  this  is 
not  so. 

5.  Again,  in  the  matrix  of  the  dento-genetic  zone  observed 
on  the  margins  of  incompletely  developed  pulps,  fibrils  are  seen 
most  clearly  to  stretch  across  the  intervening  boundary,  and 
there  is  a  distinct  mark  of  demarcation  between  them  and  the 
homogeneous  substance  through  which  they  extend. 

6.  The  granularity  of  the  cells,  as  has  been  already  stated, 
is    visibly    unaffected    by  dilute  acids  or  chemical  reagents; 
thus  it  would  seem  that  calcium  salts  enter  but  little  into  their 
composition. 

7.  After  decalcification  in  formic  acid,  the  matrix  may  be 
torn  into  laminae,  which  run  parallel  to  the  surface  of  the  pulp 
cavity,  whereas  they  would  run  at  right  angles  to  that  surface 
if  odontoblasts  formed  matrix. 

8.  The  dissimilarity  in  the  shapes  and  sizes  of  the  cells  is 
against  the  acceptance  of  this  view;  this  dissimilarity  would 
be  inexplicable  if  they  formed  dentine.     Osteoblasts  do  not 
differ  thus. 

9.  The  fact  that  nodules  of  calcine  material  in  the  pulp  are 
formed  by  small  round  cells,  and  that  odontoblasts  take  no 
part  in  this  work,  is  clearly  seen  when  sections  of  pulps  con- 
also  taining  calcareous  degenerations  are  cut  in  situ.     This  rule 
obtains  in  the  growth  of  composite  odontomes  (see  Vol.  II). 

10.  It  is  a  law  that  after  a  cell  has  ceased  its  functions,  it 


33° 


APPENDIX 


atrophies  and  disappears.     Here,  however,  odontoblasts  per- 
sist long  after  all  dentine  matrix  has  been  completed. 

11.  In  some  sections  of  the  root,  with  the  pulp  in  situ,  here 
and  there  odontoblasts  are  absent.     It  is  remarkable  that  in 
these  situations  their  corresponding  tubules  are  wanting. 

12.  And  finally   there  must  be  added  Underwood's1  state- 
ments— "that   the   distinction   between   fibril   and   matrix   is 
not  merely  one  of  a  degree  of  calcification,"  because  it  (the 
fibril)  is  equally  observable  when  the  tissue  has  been  formed 
but  not  calcified;  it  remains  after  decalcification;  it  is  present 
in  the  interglobular  spaces  where  no  calcification  has  occurred; 
"that  all  traces  of  the  boundaries  of  the  cells  are  absolutely 
obliterated  even  in  imperfectly  developed  tissue;"  and  "that 
the  cells  and  their  processes  are  sharply  marked  off  from  the 
surrounding  tissues  during  all  the  stages  of  development." 

Positive  Evidences 

In  order  to  deal  satisfactorily  with  the  evidences  which  are 
at  hand,  to  show  what  are  the  functions  of  the  odontoblasts, 
it  is  important  to  take  three  things  into  consideration,  viz., 
the  development  of  these  cells,  their  relation  to  the  nutrition 
of  dentine,  and  the  question  whether  or  not  the  ultimate  ter- 
minations of  the  nerves  have  any  direct  or  indirect  connection 
with  the  odontoblasts. 

And  here  arise  the  most  serious  difficulties  that  surround 
the  subject.  The  odontoblasts,  as  far  as  is  known,  are  derived 
from  the  stomodaeal  mesoderm,  i.e.,  they  are  formed  on  the  edge 
of  the  up-growing  papilla  of  the  dentine  organ.  If  it  could  be 
proved  that  they  arise  from  ectoderm,  one  great  difficulty  would 
be  removed,  for  it  would  be  then  quite  easy  to  affirm  that  they 
are  nerve  endings  or  end  bulbs,  and  their  analogy  to  the  cells 
at  the  terminations  of  the  optic  and  auditory  nerves  would  be 
more  striking,  not  only  with  regard  to  their  morphology  but  also 
their  physiology.  Most  authorities  agree  that  the  nervous 
system  is  produced  primarily  by  the  ectodermic  layer  of  the 
blastoderm.  Schafer  remarks  in  the  last  edition  of  Quain 

1Op.  cit.,  p.  410. 


APPENDIX  331 

(vol.  i.,  part  ii.),  "All  nerve-fibres  and  nerve-cells  .  .  .  are 
originally  derived  from  the  neural  or  neuro-sensory  ectoderm." 
If  these  statements  are  true,  one  is  led  to  the  conclusion  that 
odontoblasts  cannot  possibly  be,  from  the  developmental  point 
of  view,  ganglion  cells  in  which  sensory  or  tactile  or  trophic 
impulses  arise  de  now.  But  it  is  no  argument  against  the  idea 
that  they  serve  as  sensation  transmitters. 

Again,  it  is  difficult  to  believe  that  odontoblasts  serve  merely 
as  factors  in  the  production  of  and  keeping  up  the  nutrition 
and  vitality  of  dentine,  for,  as  has  been  pointed  out,  they  are 
practically  absent  from  the  radicular  part  of  the  pulp.  If 
this  were  their  office  there  would  be  no  diversity  of  shape  or 
size.  Dentine  is  vitalised,  in  the  opinion  of  the  author,  by  a 
protoplasmic  exudation  which  emanates  from  the  blood-vessels 
of  the  pulp,  and  fills  the  tubules  by  surrounding  and  protecting 
and  nourishing  the  fibrils.  The  pulp  capillaries  end  near  the 
odontoblasts,  but  do  not  enter  the  tubules. 

It  is  an  extremely  difficult  matter  to  have  optical  proof  that 
the  telodendria  of  the  nerves  enter  the  basal  extremities  of 
the  odontoblasts,  as  suggested  by  Aitchison  Robertson.  It 
would  be  different  if  the  nerves  did  not  lose  their  myelinic  sheaths. 
The  staining  and  demonstrating  of  these  delicate  threads 
would  then  be  quite  easy.  But  we  have  the  presence  of  the  basal 
layer  of  Weil,  which  exists  in  that  part  of  the  pulp  which  is  most 
sentient.  Pain  from  irritation  and  destruction  of  the  fibrils 
begins  in  the  crown  and  neck  of  a  tooth,  and  not  as  a  rule  under  ce- 
mentum;  and  Weil's  layer  consists  of  fine  fibres  which  extend 
deeply  into  the  pulp  on  the  one  hand,  and  into  the  basal  ends 
of  the  odontoblasts  on  the  other.  The  inference,  therefore, 
theoretically  and  logically  speaking,  is  that  many  of  the  fibres 
in  Weil's  layer  are  amyelinic  nerve  fibres.  This  can  only  be 
disproved  by  the  difficult  experiment  of  severing  the  main 
trunk  of  the  nerve  and  cutting  off  communication  with  its 
centre,  and  examining  the  pulp  for  any  degenerative  changes 
that  might  occur.  Gowers1  wrote,  "If  a  fibre  is  cut  off  from 
its  parent  cell  it  degenerates;  the  part  still  in  connection  with 
the  cell  does  not  degenerate." 

1  "Diagnosis  of  Diseases  of  Brain." 


APPENDIX 


332 

As  odontoblasts  are  largest  and  most  important  in  the  corono- 
cervical  portion  of  the  pulp;  as  their  functions  must  be  closely 
associated  chiefly  with  this  part — in  consequence  of  their  large 
size  and  importance;  and  as  this  part  is  that  through  which 
the  nerve  sensations  chiefly  reach  the  pulp  via  the  tubules, 
therefore  it  would  seem  that  the  odontoblasts  must  be  more 
intimately  connected  with  the  nervous  system  that  has  hitherto 
been  supposed,  and  they  must  be  the  actual  end  organs  or  dental 
ganglia  of  the  nerves  of  the  pulp.  And  the  corollary  is  that  the 
term  odontoblast  is  a  misnomer. 


The  Physiology  of  the  Cells  of  the  Pulp  Proper 


Little  remains  to  be  said  about  the  central  cells  of  the  pulp. 

The  functions  of  the  spindle-cells  is  probably  a  generative 
one — to  produce  new  odontoblasts  in  places  where  the  old 
cells  have  been  modified  by  the  advancing  line  of  freshly 
deposited  dentine.  The  round  cells  would  seem  to  have  a 
secretive  property,  in  cases  where  secondary  dentine  or  nodules, 
or  calcareous  degenerations  are  taking  place,  in  addition  to 
the  all-important  function  of  laying  down  the  matrix  of  dentine 
in  developing  teeth.  These  cells,  then,  should  be  called  odon- 
toblasts. 

These  researches  and  arguments  tend  thus  to  shew  what 
probably  are  the  functions  and  uses  of  the  cells  of  the  pulp; 
it  is  at  present  impossible  to  say  absolutely  that  this  view  is 
substantially  correct.  But  until  they  are  disproved,  the  reader 
may  believe  that  the  building  of  the  dentinal  wall  of  this  organ 
does  not  depend  on  the  integrity  of  the  odontoblasts,  but  on 
the  functions  of  the  small  secretory  cells  of  the  pulp  proper; 
and  that  while  the  former  are  active  agents,  governing  and 
protecting,  as  sense  or  trophic  organs,  its  interior,  their  duties 
only  ending  at  the  death  of  the  pulp,  the  latter  are  more  passive 
agents,  serving  merely  for  mechanical  purposes  by  secreting 
matrix  or  new  dentinal  formations  during  the  life  of  the  tooth. 


APPENDIX 


NOTE  B 


333 


PHYSIOLOGICAL      (LACUNAE.)      ABSORPTION     OF     THE      ALVEOLAR 
PROCESSES    OF    THE    JAWS    OF    MAN 

The  phenomena  associated  with  physiological  absorption — 
as  distinct  from  pathological  absorption  of  the  hard  tissues — 
are  observed  to  a  remarkable  extent  in  the  mouth.  The 
teeth  and  their  sockets  exhibit  these  phenomena  and  reveal 
thus  another  trait  in  their  unique  character. 

It  must  be  remembered  that  the  bone  of  the  alveolar  proc- 
esses of  the  jaws  is  a  particularly  transitory  and  unstable 
structure.  Osseous  tissue  generally  is  frequently  undergoing 
changes,  and  that  composing  the  sockets  of  the  teeth  at  an 
early  period  of  life  begins  to  show  signs  of  degeneration. 

The  teeth  of  man  are  degenerative  organs  and  their  alveolar 
attachments  also.  With  regard  to  the  latter,  five  reasons  may 
be  adduced:  (i)  Absence  of  muscular  origins  or  insertions;  (ii) 
atypical  character  of  the  structure  of  the  bone;  (iii)  poor 
or  inadequate  blood  supply;  (iv)  lack  of  function,  and  (v)  de- 
creased physiological  resistance  to  disease,  as  to  retrogressive 
metamorphoses. 

(i)  With  the  exception  of  a  few  fibres  of  the  Buccinator 
muscle  in  the  molar  region  there  are  no  reflected  or  attached 
muscular  tendons  or  fasciae  in  the  neighbourhood  of  the  teeth. 

(ii)  As  has  been  demonstrated  in  Chap.  X.,  Vol.  I,  their 
histological  elements  differ  very  greatly  from  those  of  compact 
or  cancellous  bone. 

(iii)  Near  the  terminal  margins  at  the  gum  the  m  dullary 
spaces  and  contents  of  normal  bone  are  generally  absent,  leading 
to  malnutrition  of  the  parts. 

(iv)  The  main  function  of  the  skeleton  is  to  support  the 
muscles  of  the  body.  This  function  is  certainly  lacking  here; 
the  main  function  of  the  alveolar  processes  is  merely  to  afford 
attachment,  by  a  fixed  gomphosis,  for  the  roots  of  the  teeth. 
.  (v)  As  a  consequence  of  lack  of  function,  malnutrition  and 
atypical  character,  resistance  to  disease  is  diminished  and  soon 
disappears. 


334 


APPE  XDIX 


"Physiological  absorption"  "atrophy,"  "wasting"  are  syn- 
onymous terms.  It  occurs  very  early  in  man  in  the  alveolar 
processes  of  the  jaws.  Xot  only  does  bone  undergo  this  phy- 
siological absorption  but,  as  was  described  in  Chap.  XI,  dentine 
and  cementum  do  also.  This  is  exemplified  on  examining 
a  vertical  section  of  the  jaws  of  a  young  mammal  e.g.,  a  kitten, 
before  the  deciduous  teeth  are  shed.  Absorption  areas  of 
various  sizes  can  be  easily  seen  over  the  apical  as  well  as  the 
cervical  portions  of  the  deciduous  teeth.  The  phenomenon 
is  well  observed  also  in  the  teeth  of  animals  which  have  a 
polyphyodont  dentition,  such  as  the  crocodile. 

The  same  process  occurs  through  the  operations  of  natural 
laws  in  the  deciduous  teeth  of  man.  Persistent  members  of 
this  set,  even  if  not  followed  by  any  permanent  successors,  have 
their  roots  painlessly  absorbed.  In  these  cases  the  histo- 
logical  process  would  appear  to  be  identical  with  pathological 
ones.  The  hard  parts  are  removed  by  the  agency  of  osteo- 
clasts,  and  very  frequently  the  process  of  repair  may  be  seen 
going  on  side  by  side  with  the  process  of  absorption. 

If  dried  skulls  of  children  aged  from  four  to  six  years  be  exam- 
ined, an  instructive  demonstration  of  the  condition  can  be  ob- 
tained as  it  applies  to  the  shedding  of  the  deciduous  teeth  and 
their  sockets.  There  is  here  an  obvious  physiological  absorption 
of  the  bone,  the  immediate  effect  being  the  thinning  and  destruc- 
tion of  the  tissues  by  a  method  similar  to  that  which  obtains 
in  osteoporosis.  Thus  there  is  an  entire  absorption  and  com- 
plete loss  of  the  sockets  of  the  deciduous  teeth  occurring  in  a 
normal  painless  manner.  With  regard  to  this  absorption 
Tomes1  says: — "The  alveolar  portion  of  the  jaw,  that  which 
lies  above  the  level  of  the  mandibular  canal,  is  developed 
around  the  milk  teeth;  when  they  are  lost,  it  disappears,  to 
be  re-formed  again  for  the  second  set  of  teeth,  and  is  finally 
wholly  removed  after  the  loss  of  the  teeth  in  old  age." 

The  skulls  of  adults  show  a  similar  wasting  of  bone  around 
the  cervical  and  radicular  portions  of  the  teeth.  Osseous 
atrophy  over  the  labial  surfaces  of  maxillary  and  mandibular 

1  A  Manual  of  Dental  Anatomy."  Edited  by  Marett  Tims  and  Hopewell- 
Smith,  1914. 


APPENDIX  335 

canines,  over  the  palatal  aspect  of  the  palatine  roots  of  max- 
illary molars,  as  well  as  in  other  localities  is  frequently  observed. 

The  changes  undergone  by  the  bone  of  the  mandible  are  well 
known.  Again  to  quote  Mr.  Tomes: 

"As  the  jaw  undergoes  increase  in  size,  large  additions  are 
made  to  its  surface  by  deposition  of  bone  from  the  periosteum, 
necessarily  lengthening  the  mandibular  canal.  The  addi- 
tions to  the  canal  do  not,  however,  take  place  quite  in  the  line 
of  its  original  course,  but  in  this  added  portion  it  is  bent  a  little 
outwards  and  upwards.  If  we  rasp  off  the  bone  of  an  adult 
jaw  down  to  the  level  of  this  bend,  a  process  which  Nature  in 
great  part  performs  for  us  in  an  aged  jaw,  or  if  instead  we  make 
due  allowance  for  the  alteration,  the  mental  foramen  becomes  an 
available  fixed  point  for  measurement. 

"The  manner  in  which  the  jaw  is  formed  might  also  be  de- 
scribed as  wasteful;  a  very  large  amount  of  bone  is  formed  which 
is  subsequently,  at  no  distant  date,  again  removed  by  absorption. 

''To  bring  it  more  clearly  home  to  the  student's  mind,  if  all 
the  bone  formed  were  to  remain,  the  coronoid  process  would 
extend  from  the  condyle  to  the  region  of  the  first  premolar, 
and  all  the  teeth  behind  that  would  be  buried  in  its  base; 
there  would  be  no  "neck"  beneath  the  condyle,  but  the  in- 
ternal oblique  line  would  be  a  thick  bar  corresponding  in  width 
with  the  condyle.  It  is  necessary  to  fully  realize  that  the 
articular  surface  with  its  cartilage  has  successfully  occupied 
every  spot  along  this  line,  and  as  it  progresses  backwards 
by  the  deposition  of  fresh  bone,  it  has  been  followed  up  by  the 
process  of  absorption  removing  all  that  was  redundant. 

"On  the  outer  surface  of  the  jaw  we  can  frequently  discern 
a  slight  ridge,  extending  a  short  distance  from  the  head  of  the 
bone,  but  if  the  prominence  were  preserved  on  the  inner  sur- 
face, the  mandibular  artery  and  nerve  would  be  turned  out  of 
their  course.  We  have  thus  a  speedy  removal  of  the  newly 
formed  bone,  so  that  a  concavity  lies  immediately  on  the  inner 
side  of  the  condyle;  and  microscopic  examination  of  the  bone 
at  this  point  shows  that  the  lacuntz  of  Howship,  those  charac- 
teristic evidences  of  absorption,  abundantly  cover  its  surface, 
showing  that  here,  at  least,  absorption  is  most  actively  going  on. 


336 


APPENDIX 


"In  the  same  way  the  coronoid  process,  beneath  the  base  of 
which  the  first,  second,  and  third  molars  have  successfully 
been  formed,  has  moved  backward  by  absorption  cutting 
away  its  anterior,  and  by  deposition  adding  to  its  posterior 
surfaces. 

"In  old  age,  concomitantly  with  the  diminution  of  muscular 
energy,  the  bone  about  the  angle  wastes,  so  that  once  more  the 
ramus  appears  to  meet  the  body  at  an  obtuse  angle.  But  all 
the  changes  which  mark  an  aged  jaw  are  the  simple  results  of  a 
superficial  and  not  of  an  interstitial  absorption,  corresponding 
with  a  wasting  of  the  muscles,  of  the  pterygoid  plates  of  the 
sphenoid  bone,  etc."  [The  author's  italics.] 

To  the  above,  two  further  instructive  illustrations  from 
comparative  anatomy  may  be  added.  In  Batrachia,  e.g.,  the 
frog,  the  teeth  are  attached  by  their  bases  and  external  surfaces 
to  a  groove  in  the  jaw,  having  the  external  wall  higher  than  the 
inner,  and  also  having  on  their  outer  side  a  new  osseous  forma- 
tion which  slightly  extends  over  the  outer  side  of  each  tooth. 
The  deficiency  on  its  inner  aspect  is  supplied  by  a  long  pillar, 
which  disappears  when  the  tooth  is  shed,  a  new  column  being 
developed  for  the  succeeding  tooth. 

And  even  a  more  interesting  fact  is  observed  in  the  mouth  of 
the  eel.  Here  the  teeth  are  fixed  to  the  jaws  by  means  of  a 
"bone  of  attachment."  When  the  teeth  are  shed,  the  bone  of 
attachment  is  shed  also,  being  removed  from  the  body  of  the 
jaw  itself.  This  is  effected  by  means  of  large  multi-nucleated 
giant  cells,  which  leave  the  surface  of  the  bone  scalloped  out 
into  Howship's  foveolae. 

It  is  certain  that  the  free  alveolar  edges  of  the  jaws  of  man 
begin  to  disappear  at  a  very  early  age.  Radiographs  show  the 
commencement  of  the  absorption  of  the  bone  around  the  roots 
of  the  deciduous  teeth  in  the  normal  mouths  of  healthy  children 
at  the  age  even  of  four  years.  If  radiographs  of  the  jaws  of 
healthy  and  normal  adults  aged  twenty  and  more  be  examined 
the  same  thing  is  apparent.  The  free  edges  of  the  lamina 
durce  ^disappear,  while  they  themselves  remain  in  their  other 
portions  intact. 

Examples  need  not  be  further  multiplied;  physiological  ab- 


APPENDIX  337 

sorption  is  so  obvious.  Finally  Hektoen  and  Riesman  (A 
Text-book  of  Pathology,  1901)  write: — "It  is  generally  believed 
that  anaemia  of  bone  favors  absorption  and  hinders  apposition, 
and  it  may  be  one  of  the  factors  in  these  forms  of  atrophy.  The 
atrophy  may  be  concentric  or  eccentric.  It  begins,  as  a  rule, 
at  those  points  that  are  free  from  muscular  attachments.  In 
the  calvaria  the  bone  becomes  thin,  granular  and  finely  porous, 
especially  in  the  temporal  regions.  An  atrophy  occurs  in  the 
external  table;  the  internal  may  become  rough  from  the  pro- 
duction of  new  bone.  In  the  maxillae  the  alveolar  process  may 
disappear  completely." 

Bordering  on  the  line  between  physiological  and  pathological 
absorption  of  bone,  as  witnessed  in  the  alveolar  processes,  is  that 
induced  by  the  mechanical  action  of  orthodontical  appliances 
when  a  tooth  is  moved  from  one  position  to  another.  Ab- 
sorption occurs  from  pressure,  on  the  side  opposite  to  the  oc- 
casioning force,  while  deposition  of  fresh  osseous  material  takes 
place  on  the  proximate  side. 


INDEX  TO  VOL. 


ABBOT  on  enamel,  28,  33 
Abrachiate  lacunae,  201,  202 
Absorbent  organ,  209 

Origin  of,  209 

Osteoclasts  of,  211 

Stroma  of,  209 

Absorption,  physiological,  333 
Addison  and  Appleton  on 

Growth  of  teeth  of  rat,  299 
Aitchison  Robertson  on 

Growth  of  dentine,  291 

Nerve  endings  in  pulp,  154 

Odontoblasts,  127 

Alveolar  processes  of  jaws,  bone  of,  208 
Alveolo-dental  periosteum,  166 

Black  on, 167, 168, 172, 173, 174 

Calco-spherite  spherules  of,  178 

Cells  of,  169 

Epithelial  "rests"  of,  173 

Fibres  of,  167 

Malassez  on,  174 

Measurements  of,  167 

Nerves  of,  177 

Noyes  on,  173,  178 

Origin  of,  166 

Osteoblasts  of,  173 

Osteoclasts  of,  173 

Principal  fibres  of,  167 

Sharpey's  fibres  of,  169 

Vascular  supply  of,  177 
Ameloblasts,  245,  250,  279,  281 

Cytoplasm  of,  281 
Amyelinic  nerve  fibres,  135,  145 
Andrews,  fibres  of,  282 
Andrews  on  ameloblasts,  282 

On  Nasmyth's  membrane,  9 

On  vascularity  of  enamel  organ, 

261 
Antrum  of  Highmore,  223 

"Battledore"  cells  of,  225 

Epithelium  of,  224 

Glands  of,  226 


Antrum  of  Highmore,  Goblet  cells  of, 
225 

Lining  membrane  of,  224 

Origin  of  epithelium  of,  224 

Sappey  on,  223 

Wall  of,  205 

Arnell  on  ameloblasts,  282 
Axones,  142 

"BATTLEDORE,"  cells  of  antrum,  225 
Baume  on  origin  of  lip-furrow,  235 
Beaver,  enamel  of,  94 
Bennett  on  lamellae  in  dentine,  77 
Black    on    epithelial    bodies  in   peri- 
odontal  membrane,  174 

On  gingival  gland,  174 
Bland-Sutton  on  "Glands  of  Serres," 
223 

On  development  of  ovarian  teeth, 

305 

Bodecker  on  enamel,  28,  32 

On  Xasmyth's  membrane,  10,  n 
On  nerve  endings  in  pulp,  155 
On  vascular  supply  of  antrum,  224 

Boll  on  dentinal  tubes,  69 
On  nerve  endings,  149 
On  odontoblasts,  126 
On  sheaths  of  Neumann,  69 

Bone,  structure  of,  196 

Broomell  on  cementum,  86,  89 

CANINE  fossa,  bone  of,  198 
Capillaries  of  dental  pulp,  137 
Cat,  nerves  in  dental  pulp  of,  151,  152 
Cemental  organ,  272,  302 
Cementum,  Black  on,  87 

Broomell  on,  86,  89 

Development  of,  302 

Distribution  of,  79 

Incremental  lines  of,  85 

Magitot  on,  302 

Matrix  of,  80 


339 


34° 


INDEX 


Cementum,  Measurements  of,  79 

Modifications  of,  no 

Of  opossum,  no 

Origin  of,  79 

Perforating  canals  of,  87 

Sharpey's  fibres  of,  87 

Walkhoff  on,  84 
Cheeks,  structure  of,  181 
Choquet  on  relationships  of  hard  tis- 
sues, 19 

Crescents  of  Gianuzzi,  189,  227 
Czermak,  inter-globular  spaces  of,  69 

DEMILUNES  of  Heidenhain,  189 
Dental  capsule,  212,  266 

Development  of,  272 

Fibres  of,  214 

Glands  of,  215 

Origin  of,  212 
Dental  pulp,  in 

Cells  of,  115 

Measurements  of,  1 1 1 

Nerves  of,  138 

Origin  of,  in 

Stroma  of,  130 

Vessels  of,  134 
Dentary  centre,  195 
Dentine,  49 

Aitchison  Robertson  on  growth  of, 
291 

Bennett  on,  77 

Contour  lines  of,  74 

Development  of,  287 

Distribution  of,  50 

Experiments  in  growth  of,  291 

Granular  layer  of,  71 

Growth  of,  291 

Homogeneous  layer  of,  73 

Interglobular  spaces  of,  69 

Lamellae  of,  76 

Matrix  of,  50 

Measurements  of.  50 

Measurement  of  growth  of,  291, 
295 

Modifications  of,  100 

Mummery,  on  development  of,  289 

Mummery,  on  matrix  of,  50 

Odontogenic,  fibres  of,  52 

Of  fishes,  104 


Dentine,  Origin  of,  50 

Osteo-dentine,  104 

Plici-dentine,  100 

Rose  on  varieties  of,  49 

Schreger's  lines  in,  73 

Secondary  dentine,  78 

Varieties  of,  49,  100 

Vaso-dentine,  103 

Von  Ebner  on  development  of,  289 

Waldeyer  on  development  of,  288 
Dentine  of  hake,  104 

Of  Pristis,  102 
Dentinal  tubes,  53 

Boll  on,  69 

Branches  of,  61 

Contents  of,  63 

Courses  of,  59 

Hohl  on,  69 

Klein  on  contents  of,  64 

Kolliker  on,  57,  61,  62,  67 

Lent  on,  69 

Magitot  on  contents  of,  65 

Measurements  of,  57 

Morgenstern  on  contents  of,  65 

Neumann  on,  65,  66 

Romer  on,  67 

Sudduth  on, 68 

Tomes  on,  69 

Underwood  on,  69 

Walls  of,  63,  65 
Dentogenetic  zone,  280 
Dependorf  on  innervation  of  dentine, 

154 
Development  of  dental  capsule,  272 

Of  dentine  papilla,  245 

Of  enamel  organ,  238 

Of  jaws,  195,  303 

Lepkowski  on  vascular  supply  of, 
266 

Of  osteo-dentine,  325 

Of  plici-dentine,  325 

Vascular  supply  of,  262 

Of  vaso-dentine,  325 
Development  of  teeth  in  cod  fish,  314 

Crocodile,  319 

Dog  fish,  316 

Human  embryos,  303 

Lizard,  319 

Mammals,  231 


INDEX 


341 


Development  of  teeth  in  Newt,  323 
Reptiles,  319 
Snake,  322 

EBNER    on   development   of    dentine, 
289 

On  enamel,  33 

On  enamel  spindles,  43 

On  matrix  of  dentine,  50 
Enamel,  17 

Amelo-dentinal  junction  of,  47 

Andresen  on,  33 

Andrews    on      development     of, 
282 

Appearances  of,  21 

Arnell  on  development  of,  282 

Of  beaver,  94 

Bodecker  on,  28,  43 

Bodies  of,  31 

Choquet  on  relationships  of,  19 

Development  of,  280 

Distribution  of,  17 

Encapsuled  lacunae  of,  13 

Of  fishes,  96 

Of  hare,  96 

Imbrication  lines  of,  26 

Kolliker  on,  25 

Leon  Williams  on  development  of, 
285 

Of  man,  21 

Of  manatee,  95 

Matrix  of,  32 

Measurements  of,  18 

Modifications  of,  93 

Origin  of,  17 

Of  porcupine,  95 

Of  rat,  94 

Relationships  of,  19 

Of  rodents,  94 

Of  Sargus,  97 

Schreger's  lines  in,  37 

Spec  on  development  of,  282 

Of  squirrel,  95 

Structural  modifications  of,  93 

Sudduth  on,  33,  284 

Thorsen  on  relationships  of,  20 

Tomes  on,  43,  281 

Tubular,  96,  281 
Enamel  "bud,"  238 


Enamel  organ,  ameloblasts  of,  250 

Beale  on  vascularity  of,  261 

External  epithelium  of,  244,  245, 
279 

Inner  ameloblastic  membrane  of, 
251 

Internal  epithelium  of,  245,  279 

Leon  Williams  on,  245,  251,  252, 
279 

Membrana  preformaliva  of,  251 

Stellate   reticulum   of,    240,    244, 
245,  256,  261,  279 

Stratum  intermedium  of,  241,  245, 
252,  255,  261,  279 

Vascularity  of,  261 
Enamel  rods,  21 

Abbott  on,  28,  32,  33 

Bodecker  on,  28,  32 

Curvatures  of,  34 

Ebner  on,  33 

Leon  Williams  on,  29,  31,  32,  37 

Of  man,  21 

Measurements  of,  25 

Pigmentation  of,  29 

Striae  of  Retzius  of,  35 

Sudduth  on,  33 

Tomes  on,  34 

Walkhoff  on,  32 
Enamel  spindles,  39 

Bodecker  on,  43 

Ebner  on,  43 

Hertz  on,  46,  47 

Hollander  on,  43 

Paul  on,  45 

Romer  on,  41,  44 

Tomes  on,  43 

Waldeyer  on,  45 

Walkhoff  on,  46 

Wedl  on,  43 

Epithelial  sheath  of  Hertwig,  174,  257, 
2/9 

FIBRES  of  Andrews,  282 
"Formative  ring,"  293,  294,  296,297 
Fromman's    lines    in    myelinic    nerve 
fibres,  143 

GasterostcHS,  nerves  in  dental  pulp  of, 
144 


342 


INDEX 


Gianuzzi,  crescents  of,  189 
Gingival  trough,  221 
Glands  of  antrum,  226 

Salivary,  187 

Of  tongue,  1 86 

Gobius,  nerves  in  dental  pulp  of,  144 
Goblet  cells  of  antrum,  225 
Gum,  Andrews  on  "Glands  of  Serres" 
of,  223 

Epithelium  of,  217,  220 

Glands  of,  222 

"Glands  of  Serres"  of,  223,  261 

Papillae  of,  221 

"Spiny"  cells  of,  220 

Tomes  on  "Glands  of  Serres"  of, 
223 

Vascular  system  of,  264 

HAKE,  enamel  of,  96 
Hard  palate,  bone  of,  203 

Structure  of,  191 
Haversian  systems,  196 
Hektoen  and  Riesman  on  physiological 

absorption,  337 

Hertwig,  epithelial  sheath  of,  174 
Hertz  on  enamel  rods,  34 
On  odontoblasts,  129 
Hohl  on  sheaths  of  Neumann,  69 
Hollander  on  enamel  spindles,  43 
Homogeneous  layer  of  dentine,  73 
Howes  on  vascularity  of  enamel  organ, 

261 

Howship's  foveola?  (lacunas),  209 
Huber  on  nerve  endings  in  dental  pulp, 

150 

IMBRICATION  lines  of  enamel,  25,  26 
Incisures,  143 
Intercalary  duct,  188 
Interdental  septa,  bone  of,  202 
Intralobular  duct,  187 

JAWS,  bone  of,  195 

Development  of,  195,  303 

KLEIN  on  contents  of  dentinal  tubes, 

64 
On  odontoblasts,  328 


Kolliker  on  dentinal  tubes,  61,  62,  63, 

67 

On  enamel,  25,  36,  37 
On  Nasmyth's  membrane,  1 1 
On  nerve  endings  in  pulp,  154 
On  odontoblasts,  121 

LABIODENTAL  strand,  235 

Laccrta  agilis,  nerves  of  pulp  of,  145 

Lacunae,  abrachiate,  201 
Of  bone,  197 

Lamellae  of  bone,  197 
Of  dentine,  76 

Lamina  dura,  169,  203 

Layer  of  Weil,  130 

Leche  on  origin  of  lip-furrow,  235 

Lent  on  dentinal  tubes,  69 

Leon    Williams    on    development    of 

enamel,  285 
On  enamel,  31,  32,  37 
On  secreting  papillas,  245 
On  stratum  intermedium,  245 
On  vascularity  of  enamel  organ, 
285 

Lepkowski  on  vascular  supply  of  den- 
tal tissues,  266 

Lingual  tonsil,  186 

Lips,  structure  of  181 

Lip-furrow,  234 

Baume  on  origin  of,  235 
Leche  on  origin  of,  235 
Rose  on  origin  of,  235 
Sudduth  on  origin  of,  235 

Lizard,  development  of  teeth  of,  319 

Low  on  mandible,  195 

Lymph  nodes  of  tongue,  186 

MAGITOT    on    contents    of    dentinal 

tubes,  65 

On  nerve  endings,  152 
On  odontoblasts,  127 
On  sheaths  of  Neumann,  68 
On  vascularity  of  enamel  organ, 

261 
Malassez   on   "rests"   in   periodontal 

membrane,  174 
Manatee,  enamel  of,  95 
Mandible,  bone  of,  205 
Low  on,  195 


INDEX 


343 


Marett  Tims  on  vascularity  of  enamel 

organ,  261 

Maxillary  sinus  (see  Antrum). 
Meckel's  cartilage,  195,  232 
Mice,  nerves  in  dental  pulp  of,  148 
Morgenstern    on  contents  of  dentinal 

tubes,  65 

On  nerve  endings,  156 
Mucous  glands,  189 

Crescents    of     Gianuzzi    of,    189, 

227 
Mucous  membrane  of  antrum,  223 

Of  mouth,  217 
Mummery  on  development  of  dentine, 

289 

On  matrix  of  dentine,  50 
On  nerve  endings  in  Mammalia, 

158 

Myelinic  nerves  of  pulp,  140 
Axones  of,  142 
Crosses  of  Ranvier  of,  143 
Fromman's  lines  of,  143 
Incisures  of,  143 
Internodular  segments  of,  143 
Kolliker  on,  154 
Method  of  distribution  of,  140 
Myelin  sheath  of,  143 
Neurilemma  of,  143 
Nodes  of  Ranvier  of,  143 
Schafer  on,  158 
Structure  of,  142 
Terminations  of,  144 
In  fishes,  144 
In  mammals,  148 
In  reptiles,  145 

NASMYTH'S  membrane,  9 
Andrews  on,  9 
Bodecker  on,  10 
Cellular  layer  of,  n 
Development  of,  279 
Distribution  of,  9 
Kolliker  on,  n 
Lacunae  in,  13 
Measurements  of,  10 
Origin  of,  9 
Of  ovarian  teeth,  16 
,     Paul  on,  13 

Translucent  pellicle  of,  13 


Xervous  system  of  periodontal  mem- 
brane, 177 

Of  pulp,  138 
Neumann,  sheaths  of,  65 

On  contents  of  dentinal  tubes,  66 
Neurilemma,  143 

Newt,  development  of  teeth  of,  324 
Noyes  on  alveolo-dental  periosteum, 
178 

On  osteoblasts,  173 

ODOXTOBLASTS,  116 

Aitchison  Robertson  on,  127 

Analogies  of,  129 

Boll  on,  126 

Hertz  on,  129 

Kolliker  on,  121 

Magitot  on,  127 

Paul  on,  119,  121,  122,  129 

Processes  of,  126 

Relationships  of,  121 

Rose  on,  115 

Shape  of,  116 

Size  of,  121 

Structure  of,  122 

Transitional  tissue  of,  122 

Underwood  on,  IIQ,  330 

Waldeyer  on,  121 
Odontogenic  fibres,  52 
Opossum,  cementum  of,  no 
Ortho-dentine,  49 
Osteoblasts,  173 
Osteoclasts,  173 
Osteo-dentine,  104 

Development  of,  325 
Osteoid  dentine,  109 
Owen's  lines  in  dentine,  74 
Ox,  nerves  in  pulp  of,  154 

Odontoblasts  of,  127 

PALATE,  191 

Bone  of,  203 

Papilla  palalina,  192 

Soft  palate,  191,  192 
Papilla;  of  tongue,  182 

Circumvallate  papillae,  184 

Conical  papilla;,  183 

Fungiform  papilla?,  184 

Gustatory  cells  of,  186 


344 


INDEX 


Papillae  of  tongue,  Schafer  on,  184 
Parotid  gland,  187 
Partsch  on  basal  layer  of  Weil,  132 
Paul  on  enamel  spindles,  45 

On  Xasmyth's  membrane,  13 

On  odontoblasts,   119,   121,   122, 
129 

On  tubular  enamel,  98 

On  vascularity  of  enamel  organ, 

261 
Paulton    on    vascularity    of    enamel 

organ,  261 
Periodontal   membrane    (see  Alveolo- 

dental  Periosteum). 
Periosteum  of  bone,  197 
Physiological  absorption,  Hektoen  and 

Riesman  on,  337 
Plici-dentine,  100 

Development  of,  325 
Pont  on  nerves  of  the  pulp,  160 

On  odontoblasts,  161 
Porcupine,  enamel  of,  95 
Primary  epithelial  inflection,  234,  278 
Primitive  dental  furrow,  233 
Pristis,  dentine  of,  102 
Pulp,  arteries  of,  134,  136 

Basal  layer  of  Weil  of,  130 

Capillaries  of,  137 

Cells  of,  115 

von  Ebner  on  basal  layer  of  Weil 

of,  133 
Mummery  on  basal  layer  of  Weil 

of,  132,  134 

Nervous  system  of,  138 
Partsch  on  basal  layer  of  Weil  of, 

132 

Supporting  fibres  of,  122 
Veins  of,  137 
Weil  on  basal  layer  of,  130 

RABBITS,  nerves  in  dental  pulp  of,  149 
Ranvier,  crosses  of,  143 

Nodes  of,  143 

Raschkow,  plexus  of,  140,  164 
Rat,  enamel  of,  94 

Growth  of  teeth  of,  299 
Retzius  on   nerve  endings   in   dental 
pulp,  144,  145,  148 

Striae  of  enamel  of,  35 


Romer  on  enamel  spindles,  41,  44 
On  nerve  endings  in  pulp,  153 
On  walls  of  dentinal  tubes,  67 

Rose  on  odontoblasts,  115 

On  origin  of  lip-furrow,  235 
On  varieties  of  dentine,  49,  108 

Russell's  fuchsine  bodies,  221 

Salamander  maculata,  nerves  in  pulp  of, 

148 

"Salivary  corpuscles,"  194 
Salivary  glands,  187 

Acini,  1 88 

Ducts  of,  187 

Structure  of,  187 
Salter  on  secondary  dentine,  78 

On  cementum,  86 
Sappey  on  antral  glands,  223 
Sargns  ovis,  enamel  of,  97 
Schafer  on  myelinic  nerves,  158 

On  nerve  endings,  158 

On  origin  of  nerves,  330 

On  papilla?  of  tongue,  184 
Schreger's  lines  in  dentine,  73 

In  enamel,  37 
Schultze  on  axones,  142 
Schweitzer    on    supposed    pulp    lym- 
phatics, 137 
Secondary  dentine,  78 
Serous  glands,  190 
Serres,  "glands"  of,  223,  261 
Sharpey's  fibres,  87,  169,  197,  198 
Sheaths  of  Neumann,  65 

Boll  on,  69 

Hohl  on,  69 

Lent  on,  69 

Magitot  on,  69 

Romer  on,  67 

Sudduth  on,  68 

Tomes  on,  69 

Underwood  on,  69 
Snake,    development    of     teeth     of, 

322 

Spec  on  ameloblasts,  282 
Spiny  cells  of  gum,  220 

Of  Nasmyth's  membrane,  13 
Squirrel,  enamel  of,  95 
Stratum   intermedium,    241,    245,    252, 
255,  261,  279 


INDEX 


345 


Stellate  reticulum,  240,  244,  245,   256, 

261,  270 

Stohr   on    alveolo-dental    periosteum, 
1 66 

On  cementum,  87 
Sublingual  gland,  187 
Submaxillary  gland,  187 
Sudduth  on  enamel,  33 

On  sheaths  of  Neumann,  68 
Sympathetic  nerves  of  pulp,  144 

TOMES  on  dentine,  49,  70 
On  dentinal  tubes,  69 
On  enamel,  34,  281 
On  enamel  organ,  261 
On  enamel  "spindles,"  43 
On  "glands  of  Serres,"  223 
On  odontoblasts,  327 
On  osteo-dentine,  108 
On  physiological  absorption,  334, 

335 

On  sheaths  of  Neumann,  69 
Tongue,  glands  of,  186 

Lymph  nodes  of,  186 

Muscles  of,  181 

Papillae  of,  182 

Taste  buds  of,  186 
Tonsils,  lymphoid  cells  of,  193,  194 

Lymphoid  follicles  of,  193 
Tooth-band,  234,  278 
Trabecular  dentine,  108 


Translucent     pellicle     of     Nasmyth's 

membrane,  13 

Triton  cristatus,  nerves  of  pulp  of,  148 
Tubular  enamel,  96 

UNDERWOOD  on  cementum,  90 
On  odontoblasts,  119 
On  sheaths  of  Neumann,  69 

Uvula,  structure  of,  192 

VASCULARITY  of  enamel  organ,  261 
Vaso-dentine,  103 

Development  of,  325 
Vitro-dentine,  49,  108 
Vitro-trabecular  dentine,  109 
Veins  of  the  pulp,  137 

WALDEYER  on  development  of  dentine, 
288 

On  enamel  spindles,  45 

On  odontoblasts,  121 
Walkhoff  on  cementum,  84 

On  Dental  Histology,  4 

On  enamel,  32 

On  enamel  spindles,  47 

On  odontoblasts,  327 
Wedl  on  vascularity  of  enamel  organ, 

261 

Weil,  basal  layer  of,  130 
Welcker  on  dentinal  tubes,  60 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 

Los  Angeles 
This  book  is  DUE  on  the  last  date  stamped  below. 


MAR  2 


•fa, ,  .- 
JUN  2  4REC'0 


1973 


PormL9-40m-5,'67(H2161s8)4939 


3  1158  00346  7031 


DC  SOUTHERN  REGIONAL  LIBRARY  FACILITY 


A    000  373  735     0 


